A List of 90 Best Online Dictionaries: Stock up on New Words!

Dictionaries are here to stay.

Here’s the thing:

Whether you are learning a new language, reading an article in a science magazine or enjoying an old book, you are going to need a dictionary. These days, there is no need to carry around a humongous volume of the Macmillan Dictionary. All it takes is a smartphone or a laptop.

And, luckily, you won’t have to waste your time and browse on Google for online dictionaries on a variety of subjects.


Because Custom Writing team already has compiled the best of them in the list below. Sophisticated terminology, regional dialects, obscure slang, comprehensive commentary with guide words — it’s all in here.

📕 Monolingual Dictionaries

Here you will find a list of online English dictionaries that can help you understand the meaning of any word that gives you trouble.

British English

If you are planning a visit to the land of custard and cabs, these two dictionaries should be your first choice.

The oldest word in English fact.
  1. Cambridge Dictionary. Essential British English
    The Cambridge Dictionary has concise definitions, transcriptions, and audio pronunciations. With well over 18,000 entries, it is a safe place to search for the most obscure words. Especially if you want to become a Scrabble champion.
  2. British English Dictionary Add-On
    This add-on is especially helpful to people who don’t like to get distracted by a dozen tabs open in their browser. With this add-on, the meaning of any word will always be easy to find.

American English

Ready to explore English as it is spoken in the United States? Here are some online resources to help you out:

  1. New Oxford American Dictionary
    Oxford Dictionaries are not dedicated solely to the British variety of English. With this add-on, the correct definition is just one click away.
  2. Heinle’s Newbury House Dictionary of American English
    This one combines a comprehensive dictionary and thesaurus with plenty of synonyms common in the US. Multiple examples and user-friendly interface make it the right choice for anyone curious about American English.
  3. Cambridge Dictionary. Essential American English
    The online version of the Cambridge Dictionary is one of the most popular online English dictionaries. With almost 15,000 definitions that are written in simple language, this dictionary is perfect for beginning learners of English.
  4. Dictionary of American Regional English
    DARE is a go-to dictionary if you have planned a trip across the country and want to be able to speak the language of any state from Minnesota to Florida. Quaint phrases, peculiar idioms, familiar words with surprising new meanings — it’s all in here.

Canadian English

While in certain ways English, as Canadians speak it, is similar to its US version, there are significant differences you don’t want to miss out on.

Canadians call English their mother tongue fact.
  1. A Dictionary of Canadianisms on Historical Principles
    This dictionary was put together by The University of British Columbia. As the name of the dictionary suggests, it shows the way meanings of various words and phrases have changed over multiple decades.

Australian English

  1. Macquarie Dictionary
    The “Aussie” variety of English is quite something: far from its US and United Kingdom counterparts. Australian English can seem a bit quirky, but its colloquialisms and curious idioms are surely worth learning.

New Zealand English

  1. NZ English to US English Dictionary
    While similar in many respects to Australian English, New Zealand English has enough quirks and odd phrases to warrant a dictionary.

Singaporean English

  1. Dictionary of Singlish
    Singlish is a unique variety of English that has experienced the influence of Chinese, Indian and Malay languages. Therefore, a considerable amount of its vocabulary and phraseology can be almost impossible to understand without a dictionary of English to English translation like this.

Various English Dictionaries

Longest word in English.
  1. Oxford English Dictionary
    The online version of the undisputed masterpiece of lexicography is a treat for everyone who wants to dive right into the magnificent world of English. With tens of thousands of entries and detailed descriptions, it’s one of the best dictionaries out there.
  2. Dictionary.com
    Simple interface, words of the day, etymologies and even a difficulty index for all words. Dictionary.com is great for anyone looking for modern definitions.
  3. Collins Online Dictionary
    This classic dictionary has made a successful transition to the digital space. Collins Online Dictionary has over 700,000 words. On top of that, there are constant updates to the dictionary. You can always count on seeing the latest neologisms.
  4. Macmillan Dictionary
    The Macmillan English dictionary will undoubtedly satisfy any advanced learner of English. It provides users with all the necessary grammatical information and collocations.
  5. Merriam-Webster Dictionary
    The history of this dictionary spans almost two centuries. With interesting information on the history of words and the usage of trending words, it’s one of the best dictionaries online.
  6. The WordReference English Dictionary
    This online dictionary uses the resources of several classic dictionaries in English and provides the reader with concise definitions and simple examples.
The WordReference English Dictionary website fact.
  1. The Free Dictionary
    If you are looking for extensive coverage of any term with etymology, look no further. Here you will find literal and figurative meanings of words, as well as their usage in phrasal verbs and idioms. A real gem for students of English.

🙂 Slang Dictionaries

Formal language is fine and all, but once you are out on the streets of East-Side or Chicago, you need to update your vocabulary. In these dictionaries, you will find all the colloquial phrases that will show those around you that you are “in.”

  1. Australian English Slang
    Koala.net put together this excellent dictionary for all those wondering how these folks down under speak. The creators of this dictionary focused specifically on Australian colloquialisms and excluded slang words that are widely used in other parts of the English-speaking world.
  2. Browse the aussie slang dictionary
    A very simple yet comprehensive list of Aussie sayings and words used in everyday life. Some of them might come off as a bit crude; some of them are funny. But if you want to have a nice chat in the streets of Sydney or Melbourne, make sure you take a look at this dictionary first.
  3. English slang and colloquialisms used in the United Kingdom
    The best thing about this slang dictionary is that it is updated at least once a month. With the variety of various vernaculars all across the United Kingdom, this dictionary includes slang and jargon common in many areas. Aside from useful new entries, it contains a wide range of expressions that are almost obsolete but still curious to learn.
  4. British English Slang Dictionary
    The authors of this dictionary claim that it’s the biggest online dictionary of UK slang. Whether it’s technically true or not, this website will be of particular interest to you if you are more familiar with American English.
Use of slang in Britain dates back to before 16th century.
  1. British Slang Dictionary
    There’s a reason this online dictionary has a “Made in Britain” stamp on the main page. Entries in this dictionary can only be approved if edited by Native Speakers of British dialects.
  2. Commonly-Used American Slang
    Reasonably concise and straight to the point, this dictionary doesn’t have long-winded definitions and explanations. But it does provide helpful examples. It also has the kind of interface that makes it particularly useful to English learners who want to test their knowledge of various colloquialisms.
  1. Cockney Rhyming Slang Dictionary
    According to the creators of this website, it is the most comprehensive guide to cockney rhyming slang. One thing for sure: it is enormous. It has colorful comic-strip style illustrations and a fun rating system.
  2. The Online Slang Dictionary
    Being as this is one of the oldest online dictionaries on the Internet, The Online Slang Dictionary can boast of almost 25,000 definitions. Every entry has a detailed description containing several definitions. There are also three helpful rating scales based respectively on how common the word is, how vulgar it is and where it is used most.
Slang maps in the online slang dictionary.
  1. Dictionary of Internet Slang
    Are you completely baffled by some bizarre phrase or word you saw on the Internet? Even an experienced Internet user is not immune to that. This online dictionary has a ton of fascinating vocabulary that will allow you to blend in with any obscure Internet subculture. Abbreviations, acronyms, weird idioms — it’s all here.

🎁 Specialized Dictionaries

Sometimes, a regular dictionary is simply not enough. Occasionally, you need something more specific and to the point. Maybe you want to learn some professional jargon, or you are puzzled by some very obscure and little-known term. In any case, you have plenty of specialized dictionaries to choose from.

Military Dictionaries

NACHOS in military jargon.
  1. Department of Defense Dictionary of Military and Associated Terms
    This dictionary is particularly useful as it is the primary source of military terminology for all levels of the DOD.
  2. The MilitaryFactory.com
    Another military dictionary with terms widely used within the DOD. User-friendly interface and alphabetical order.

Navy Dictionaries

  1. America’s Navy Acronyms
    A short but informative glossary with the most common nautical acronyms used in the US Navy.
The professional jargon used in the US Navy.
  1. Glossary of German Navy Terms
    Want to learn the professional jargon of the German Navy? Start with this dictionary. It also includes a list of commonly used German acronyms.
  2. Glossary of Nautical Terms: English French, French-English
    This dictionary was approved by the US Coast Guard, meaning this one will be a decent choice.

Biology Dictionaries

  1. Biology Online Dictionary
    This dictionary contains detailed explanations of biological and medical phenomena, and each entry has a list of related terms.
  2. Biology Dictionary
    Here you will find a lot of biological terms organized in various categories depending on the specific field of study.
  3. Macroevolution Online Biology Dictionary
    This regularly updated dictionary has plenty of information on evolutionary biology, medicine, anatomy, molecular biology and many other biological disciplines. Nuanced illustrations help readers grasp complex concepts, and those who want to learn more can use the website’s encyclopedia of biology.

Physics Dictionaries

  1. Physics and Relativity Dictionary
    Whenever you find something perplexing about any of the relativity theories or quantum physics, you should consider consulting this dictionary.
Edward Teller quote.
  1. Physics and Astronomy Glossary
    It’s a short yet detailed glossary of astronomy-related terms. It’s going to work best for those who are not content with the way standard dictionaries describe vocabulary specific to astronomy. Also, it can be very helpful to students writing science and technology essays.

Math Dictionaries

  1. Illustrated Mathematics Dictionary
    This dictionary has easy-to-grasp definitions, helpful illustrations and a lot of useful information on algebra and geometry.
  2. Online Coolmath Dictionary
    If you are looking for an illustrated math dictionary for children, this dictionary will surely come in handy. With simple explanations and colorful visuals, it is perfect for kids who want to learn the basics of math.
  3. Visual Mathematics Dictionary
    Another kid-friendly illustrated online dictionary. Entries have visual representations of various mathematical concepts. With pictures, learning math becomes much more accessible.

Architecture Dictionaries

  1. A Dictionary of Architectural Terms
    Have you ever looked at a beautiful castle or a magnificent cathedral and not known how to describe it? This dictionary will help you rectify the matter.
  2. A Dictionary of Military Architecture
    This dictionary is devoted to various terms related to fortification and military architecture throughout the centuries.

Dictionaries of Idioms

An idiom is a cunning and treacherous thing: you can’t just derive the meaning from the context of this kind of phrase. Most of the time, it’s about knowing the meaning of the whole expression, not the details.

Flula Borg quote.
  1. Idiom Site Dictionary
    A short dictionary for beginners who want to catch up on their English phraseology.
  2. The Idioms. Largest Idioms Dictionary
    An enormous library of idioms arranged in alphabetical order and by topic. Any user can submit an entry, but it is only included after being vetted by the editors.

Philosophy Dictionaries

  1. Dictionary of Philosophy
    Concise and informative entries dedicated to Western and Oriental schools of philosophy.
  2. Internet Encyclopedia of Philosophy
    This dictionary is one of the most popular web resources dedicated to philosophy. With staff consisting of people with doctoral degrees, it is one of the most reliable dictionaries on philosophy.
  3. A Dictionary of Philosophical Terms and Names
    Here you will discover plenty of useful information on philosophical ideas and famous philosophers.
Bertrand Russel quote.

Financial Dictionaries

  1. Investopedia
    This online dictionary can boast of an enormous library of entries dedicated to finances, investment and the stock market.
  2. Financial Glossary: Dictionary, Finance, Investment
    If you have only recently started to learn about all the intricacies of the world of big finance, take a look at this financial glossary.
  3. The Economic Times Financial Terms and Definitions
    This is an electronic dictionary by one of the most popular business papers in the world: The Economic Times. This dictionary is strongly recommended for those who want to read news about the economy without being puzzled by every other word.
  4. Investing Answers’ Financial Dictionary
    A continually updated dictionary for investors, analysts, and finance students.
  5. A Dictionary of Financial Terms by World Finance
    A financial compendium with a simple and intuitive design.
  6. Financial Dictionary by New York Institute of Finance
    A glossary of financial terms by one of the leading financial education organizations.
  7. Compass’s Financial Dictionary
    A concise dictionary for those curious about basic financial lingo.
Tyler Cowen quote.

Business Dictionaries

  1. Dictionary of Management, Business and MBA Terms
    While registration is required to use this dictionary, this website doesn’t charge its visitors and provides them with an extensive library of management terms, including some very obscure ones.
  2. Globaledge.msu.edu
    This online dictionary offers users precise definition, lists of related terms and a flashcard system for those who want to test how good they are with business terminology.
Andy Warhol quote.
  1. Beef Performance Glossary
    Want to know more about the language of the US meat industry? This dictionary is a good start.

Sports Dictionaries

Having trouble understanding your friends when they are watching games on TV, talking loudly in something that sounds like a foreign language? These dictionaries will help you update your sports vocabulary.

  1. SportsDefinitions.com
  2. Football: Glossary and Terms
  3. A-Z of Golfing Terms and Jargon
  4. Soccer Terms Glossary
  5. Rugby League Glossary
  6. Dictionary of Chess Terms and Definitions

Other Specialized Dictionaries

  1. Collocations Dictionary
    If you are not sure about the proper lexical context of a word, consult this resource first. Read this dictionary to make sure you use every word appropriately.
  2. Dictionary of Phrasal Verbs
    Since phrasal verbs are regularly used in informal communication, you would do well to learn some of them with this dictionary if you want your speech to sound natural.
  3. Chemistry-Dictionary.com
    With almost 2,000 chemical terms, this dictionary will help any student trying to further their knowledge of chemistry.
Michio Kaku quote.
  1. Dictionary on Environmental Chemistry
    This dictionary will be of use to anyone interested in ecology. If you want to write an essay about the environment, it is a terrific resource.
  2. Legal Dictionary
    Are you having a hard time telling apart a subpoena and a summons?
    If that’s the case, check out this legal dictionary. With a variety of legal terms and definitions, it will prove useful to anyone curious about the practice of law.

📚 Bilingual Dictionaries

These websites will provide the necessary assistance to any user who wants to find accurate translations from a specific language.

  1. Russian lessons: English to Russian Dictionary
    A comprehensive online dictionary based on one of the most popular English-Russian dictionaries by V. K. Mueller.
  2. QuickDic German to English, English to German Dictionary
    Over 300,000 words, expressions, and common phrases. A wide range of settings for those looking for precise dictionary search results.
  3. English-French Dictionary
    A simple French dictionary with straight-to-the-point translations. This dictionary works excellently for beginners and advanced learners alike.
  4. English-Irish Dictionary
    Almost 50,000 entries with grammatical information and sound files with pronunciation.
  5. SpanishDict: Spanish to English, English to Spanish Dictionary
    Over 1 million translations with examples, common phrases, and definitions.
  6. Jisho Japanese-English Dictionary
    A Japanese dictionary with highly detailed entries featuring multiple synonyms and examples of usage.
  7. Portuguese-English Dictionary
    Thousands of words, direct and indirect translations, featuring most searched and latest searches.
  8. Valley Trail English-Dutch-English Dictionary
    An illustrated dictionary with multiple words which are organized in semantic categories for readers’ convenience.
Fact about dutch language.
  1. English to Arabic to English Dictionary
    An A-Z Arabic dictionary that is essentially a huge glossary of Islam. This one will prove irreplaceable to anyone learning Arabic or studying the Quran. It features helpful apps for iPhone and Android.

🎍 Dictionaries of Uncommon Languages

Popular languages are a lot of fun to learn, not to mention their practical utility. But what about some less common ones which are not spoken all across the world, but still present an exciting challenge? They, too, have some online dictionaries.

Count of estonians in the world.
  1. Estonian-English-Estonian Dictionary
    While Estonians are a relatively small ethnic group, the fascinating folklore and history of this nation undoubtedly warrant the studying of this language.
  2. Zulu-English-Zulu Dictionary
    Are you looking for something unconventional and exotic? Try Zulu, a fascinating language with a tonal system.
  3. English-Albanian-English Dictionary
    A bit minimalistic, this dictionary will work best for advanced learners.
  4. English-Catalan Dictionary
    A native language to over 4 million people, Catalan is spoken in Catalonia, Andorra and some parts of Italy. While quite simple, the dictionary gives the necessary basic information.
  5. Esperanto Dictionary
    This is a treat for everyone eager to learn the most popular constructed language.

📓 Thesauruses

This thesaurus is one of the most popular resources of its kind. Not only does it give the reader plenty of synonyms and antonyms, but it also lists useful examples and semantically connected words. Remember, though, that if you’re looking for a thesaurus to chage up some sentences in your essay, a faster alternative might be a phrase rewriter that will alter your writing in seconds.

  1. Thesaurus.com
    This thesaurus is one of the most popular resources of its kind. Not only does it give the reader plenty of synonyms and antonyms, but it also lists useful examples and semantically connected words.
  2. Graph Words Online Thesaurus
    What makes this thesaurus particularly appealing is its interface and colorful visual approach to explaining the meaning of words. Different related words are presented in the form of a well-structured network of interconnected elements.
Steven Wright quote.
  1. Collins English Thesaurus
    This online thesaurus was put together by the professionals behind Collins Dictionary, meaning this is undoubtedly a trustworthy source.
  2. Oxford English Thesaurus
    Here you will find plenty of useful synonyms and examples with appropriate explanations.

📜 Multilingual Dictionaries

Are you looking for resources that go beyond just one language? Do you want to broaden your linguistic horizons and learn how a word is translated into several languages? Then there are a few excellent online dictionaries to choose from:

  1. Logos Dictionary
  2. Kdictionaries
  3. WordReference Multilingual Dictionary
  4. Dict.cc
  5. Dictionary of Romanian to English, German, French, Spanish, Italian

Further reading:

This article was developed by the editorial team of Custom-Writing.org, a professional writing service with 3-hour delivery.
Comments (2)

Saayoni Ghosh
Saayoni Ghosh

very helpful article. The separation based on the categories of the dictionary is the best.


Jesse Thistle spent more than a decade on the streets and in jail. But despite this he has managed to become an expert on the culture of his Indigenous