Oxford English Dictionary

An authoritative dictionary that provides the definition and pronunciation of words from the English language. Subscribers can access the online dictionary and make use of worksheets and quizzes. The Word of the Day feature can help you expand your knowledge of the English language.

http://www.oed.com/

Wordsmith.org

A website dedicated to the magic of the words. The site's main feature is a “Word of the Day” feature, accessible by email subscription, and which helps to expand your vocabulary. The Worldlovers' Library Project gives copies of "Another Word a Day" for free to libraries and schools around the world.

http://www.wordsmith.org

The Phrase Finder

This website on English words and phrases provides definitions and origins on more than 1,200 English sayings, phrases and idioms. The site also has a phrase thesaurus, a useful tool for professional writers. You can make use of the "a phrase a week" function to learn new phrases.

http://www.phrases.org.uk/

Cambridge Dictionaries Online

A reference service provided by Cambridge University Press. The five dictionaries available here focus on those learning English or wishing to translate it into Spanish and French. There is also a reference service on American English.

http://dictionary.cambridge.org/

Word Origins

Dedicated to the art of etymology, studying the origins of words. The site has reviews of word origin books and other resources that will be of interest to those who want to research word origin in depth. The blog format of the website also makes it easy to learn about word history.

http://www.wordorigins.org/

Merriam Webster

Merriam Webster is a reference website. You can use the site's dictionary, thesaurus and other tools to improve your fluency with English. The site also provides access to the Encyclopedia Britannica, one of the world's most reliable reference sources.

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

RhymeZone.com

RhymeZone is a rhyming dictionary and thesaurus that helps you find all kinds of information on rhymes. You can search for rhymes and other sayings through the site's search function. If you want to share your opinion, you can do so through the site's forum.

http://www.rhymezone.com/

The Free Dictionary

Look up words, acronyms, idioms as well as legal, medical and financial terms. The "Word of the Day" feature helps improve your vocabulary. The site's appearance can be customized to suit your needs.

http://www.thefreedictionary.com/

The Word Detective

The online edition of a humorous newspaper column about words and language, written by Evan Morris. You can read the latest issue of The Word Detective and access a large archive of earlier columns. You can also join the notification list so that you can be informed of new columns whenever they are added to the site.

http://www.word-detective.com/

MedTerms

A medical dictionary that defines a variety of medical terms. The site helps people understand the special terminology used by physicians and medical researchers, and can be searched by word or browsed. You can also access the site's “Word of the Day” feature by RSS feed.

http://www.medterms.com/