Merriam-Webster Dictionary
Free online dictionary, thesaurus, spanish-english and medical dictionaries, audio pronunciations, Word of the Day, word games, and many more.
http://www.merriam-webster.com/
OneLook Dictionary
OneLook indexes hundreds of online dictionaries, encyclopedias, and other reference sites. Searches different online resources at a time. It also provides reverse dictionary, meaning, user can provide different terms related to just one term and OneLook searches its index to provide the term user is looking for.
http://www.onelook.com/
Dictionary.com
Largest free dictionary and trusted online dictionary. Users can quickly find accurate definition, audio pronounciations, and subscribe to word of the day via email.
http://dictionary.reference.com/
Macmillan Dictionary
An online dictionary, regularly updated and with integration of thesaurus in the entries.
http://www.macmillandictionary.com/
