Visuwords™ uses Princeton University’s WordNet, an opensource database built by University students and language researchers. Combined with a visualization tool and user interface built from a combination of modern web technologies, Visuwords™ is available as a free resource to all patrons of the web.
Here are some useful dictionaries to start with:
Links to full text dictionaries, including foreign languages, subject areas, and the English language.
While not as comprehensive as other sources, this is a good quick reference site from an authority in dictionary publishing.
OneLook is a meta-dictionary. Enter an English language word or acronym, and OneLook will search its index of over 900 general and special interest dictionaries for the definition.
Provides a variety of links to specialized subject dictionaries in many different areas.