ARTFL Project: ROGET Form
Astronomy Thesaurus - astronomy terms in English, French, German, Spanish and Italian; all terms cross referenced.
Getty Art and Architecture Thesaurus - searchable database of vocabulary and terms for describing objects, textural materials, images, architecture and material culture from antiquity to the present.
Getty Thesaurus of Geographic Names - a structured vocabulary developed primarily for the field of art history, but with the potential for wide applications in related disciplines such as archeology, history, and geography.
HIV/AIDS Treatment Thesaurus - standardized bilingual (French and English) tool, created to organize and find information in the field of HIV/AIDS treatment information. Non-preferred terminology covers variant spellings.
Lexical FreeNet - this program allows you to search for rhymes and relationships between words and concepts that might never have occurred to you.
Library of Congress Thesauri
Merriam-Webster Thesaurus
NASA Thesaurus
Plumb Design Visual Thesaurus - an exploration of sense relationships within the English language. By clicking on words, you follow a thread of meaning, creating a spatial map of linguistic associations.
Roget's Thesaurus
Synonyms Dictionary
Thesaurus Gopher
Web Directory: Web Thesaurus Compendium