The best online dictionaries are not the only kind of dictionary that an ESL learner needs while studying English. To have one actual print-form dictionary constantly on hand, that you place in your backpack or bag, is one of those musts for any ESL student. However, when you are at your desk and on your laptop, there are a huge amount of resources online. The great thing about these sites is that they run from good general dictionaries and thesauri to specialized references to medical terms, legal terms, definitions, abbreviations and acronyms – you think  of it, and the web has it. There is even a dictionary which aggregates all the content of other dictionaries.  It has 19,633,003 words in 1061 dictionaries indexed – surely this is the best of the best online dictionaries.

best online dictionaries

with thanks to www.refseek.com
abbreviations.com  – directory for acronyms and abbreviations, with over 750,000 definitions.
acronymfinder.com –  all acronyms
answers.com –  definitions, encyclopedia entries, and language translations.
dictionary.cambridge.org
computerlanguage.com – computer lingo
definitions.net –  definitions and translations.
synonyms.net – dictionary of synonyms
dictionary.reference.com –  a thesaurus (facts and definitions)
thesaurus.com  – another online thesaurus
investorwords.com – financial terms
dictionary.law.com – legal terms
macmillandictionary.com – good dictionary
marketingpower.com – marketing terms
mathworld.wolfram.com – math terms
medterms.com – medical terms
medilexicon.com – medical, health, hospital industry terms
m-w.com – Merriam Webster Dictionary
visual.merriam-webster.com – 6,000 full-color images
netlingo.com – technology and communication terms
onelook.com – meta-search tool with 13 million words from 1,000 dictionaries.
oxforddictionaries.com – dictionary
thesaurus.com –  synonyms, antonyms, and brief definitions.
thefreedictionary.com – general plus legal, medical scientific term
urbandictionary.com – slang terms
visualthesaurus.com – visualization of connections between words.
vocabulary.com – dictionary
dictionary.webmd.com – medical
webopedia.com – technology, computer and internet terms
en.wiktionary.org – multilingual dictionary written and edited by the public
wordspy.com – blog tracking new words and phrases in popular use.
wordnik.com – aggregator of definitions, images, and word usage statistics.
yourdictionary.com – aggregator of definitions, thesaurus entries, spelling, pronunciation, and etymology results.

The best online dictionaries are not the only kind of dictionary that an ESL learner needs while studying English. To have one actual print-form dictionary constantly on hand, that you place in your backpack or bag, is one of those musts for any ESL student. However the specialisation that the best online dictionaries can offer makes them particularly useful.