Language Dictionaries Online: A Guide: English Language

Includes the M-W Collegiate Dictionary and Thesaurus.
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.

The premier historical dictionary of the English language. Entries for each sense of the word are illustrated with quotations from the full extent of written English.

3rd edition. New York: Oxford University Press, 2010.
With more than 350,000 words, phrases, and senses, and hundreds of explanatory notes, this dictionary provides comprehensive and accurate coverage of American English. Based on the two-billion-word Oxford English Corpus and the citation files of the Oxford English Dictionary.

3rd edition. New York: Oxford University Press, 2015.

Collected in one place, online access to Australian Oxford Dictionary, 2nd ed.; Canadian Oxford Dictionary, 2nd ed.; New Oxford American Dictionary, 3rd ed.; The New Zealand Oxford Dictionary; Oxford Dictionary of English, 3rd ed.; and two Oxford English-language thesauri.

A source of newly-coined English-language words and phrases, existing words and phrases that have been revived, and older words and phrases that are being used in new ways. Like the OED, Word Spy provides illustrative quotations of the words cited.