Online Dictionaries
Dictionary.com
Dictionary.com is a multi-source dictionary search service produced by Lexico Publishing Group, LLC, a leading provider of language reference products and services on the Internet.
   
Merriam-Webster Online
Merriam-Webster is America's foremost publisher of language-related reference works. The company publishes a diverse array of print and electronic products, including Merriam-Webster's Collegiate® Dictionary, Eleventh Edition—America's best-selling desk dictionary—and Webster's Third New International Dictionary, Unabridged.
   
MSN Encarta : Dictionary
The MSN Encarta dictionary provides over 400,000 entries, some with a pronunciation key, so you can hear how the word is spoken. In addition to definitions, dictionary entries may include word histories and word usage notes.
   
The Free Dictionary
English, Medical, Legal, Financial, and Computer Dictionaries, Thesaurus, Acronyms, Idioms, Encyclopedia, a Literature Reference Library, and a Search Engine all in one!