EAL (formerly ESL): Dictionaries and Word Finders

OneLook (*Dictionary aggregator):

http://www.onelook.com/

“A real discovery, this online site trawls 18,967,499 words in 1,060 different dictionaries – all the major English ones, but also dictionaries for specific subjects (business, art, medicine) or languages. You can customise your search – only in slang, for example; compare entries in different dictionaries; do a wildcard search (asterisks, hashtags or @ symbols account for the characters you can't remember), or a reverse search (type in "being tried twice for the same crime", for "double jeopardy", for example).” (theguardian.com)

Oxford:

https://en.oxforddictionaries.com/

This site is not only features a dictionary, but also has a language blog, as well as a thesaurus, grammar tips, word origins and interesting word lists.

Merriam-Webster:

https://www.merriam-webster.com/

“The free online equivalent of the print version of this standard college dictionary and thesaurus.  Audio pronunciations of all headwords. Site also has Word of the Day feature with the definition, example sentence, audio pronunciation, and word history section. You can subscribe to the e-mail version or just check the site. Current year archived. This site contains advertising.”  (Michael Engle, Cornell Library)

Macmillan:

http://www.macmillandictionary.com/

“The definitions are short and to the point, with no information about sources or background (though there are sample phrases, and a direct link to a thesaurus). It also lets you submit words of your own, and gives you the option of British or American English. Macmillan's particular wheeze, useful to learners of English, is to highlight the 7,500 core, high-frequency words in the English language: three-star words are the most frequent; one-star words less so.” (theguardian.com)

Chambers:

http://www.chambersharrap.co.uk/chambers/features/chref/chref.py/main

“The Chambers 21st Century Dictionary, with its 75,000 words and phrases and 110,000 definitions, is free online … with quite satisfying lists of definitions, and examples of the word in context.  A little bit of etymology, too.” (theguardian.com)

Word Spy:

http://resolver.library.cornell.edu/misc/4952424

“An excellent source of newly coined words, existing words that have been revived, and older words that are being used in new ways. Like the Oxford English Dictionary (OED), Word Spy provides illustrative quotations of the words cited.” (Michael Engle, Cornell Library)

Longman Dictionary of Contemporary English:

http://www.ldoceonline.com/

There are lots of examples of how words are used in context in this dictionary; both British and American pronunciations are provided for words. For verbs, there are also convenient tables to clearly show the different tenses.

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Grammar points from Oxford:  see https://en.oxforddictionaries.com/grammar/

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WordNet thesaurus: