Dictionaries

Medical Dictionary: National Institutes of Health
Definitions of terms related to medicine, nursing, psychology, and pharmacy

Merriam-Webster Online
Merriam-Webster Online includes a dictionary, a thesaurus, and audio files to help with pronunciation

Modern Languages: Oxford Reference Online
Spanish, French, German, and Italian dictionaries plus much more

Oxford English Dictionary
Definitions, origins, and quotations showing each word's range of meanings from the time it entered the language to the present