ARTFL Project: Roget's Thesaurus - based on Roget's Thesaurus version 1.02 (supplemented: July 1991).
Roget's Internet Thesaurus - Well designed thesaurus from thesaurus.com.
Roget's Thesaurus - Thesaurus provided by Project Gutenberg based on the version of Roget's Thesaurus published in 1911.
Web Thesaurus Compendium - A directory of online thesauri.
WordNet - "Lexical database" developed at Princeton University.
keywords: thesaurus thesauri thesauruses