Dictionary.com
Free online English dictionary, thesaurus and reference guide, crossword puzzles and other word games, online translator and Word of the Day.
dictionary.com

Art and Architecture Thesaurus
A structured vocabulary for describing and indexing the visual arts and architecture.
getty.edu

Merriam-Webster's Thesaurus
Searchable online thesaurus from Merriam-Webster.
merriam-webster.com

Babynames Thesaurus
You can search for a name from its meanings. The site has more than 10,000 names with meanings.
yourbabysname.com

Merriam-Webster's Word of the Day
A searchable dictionary and thesaurus. Includes word games, daily word with its meaning, history, usage in sentences, and etymology.
merriam-webster.com

NASA Thesaurus
National Aeronautics and Space Administration Thesaurus. Extensive coverage of scientific terms.
sti.nasa.gov

HyperDic
Based on the WordNet lexical database and thesaurus, covers a selection of the most frequent English words. Includes synonyms, antonyms, examples and pronunciation and more.
hyperdic.net

WordWeb
A free English thesaurus and dictionary for Windows.
wordweb.co.uk

beetfoundation.com Dictionary and Thesaurus
General purpose online English language dictionary and Thesaurus.
beetfoundation.com

Concept Space: the visual search tool for business concepts
A British business education thesaurus with an intriguing navigational component from the London Business School.
conceptspace.london.edu

Wordsmyth
American English dictionary with an integrated thesaurus and other lexical resources.
wordsmyth.net

Agrothesaurus
Latin-Slovenian-English glossary of plants and animals.
agroweb.bf.uni-lj.si

Getty Thesaurus of Geographic Names
Structured vocabulary of place names.
getty.edu

The Astronomy Thesaurus
Astronomical terms. Searches may be performed in English, French, German, Italian, and Spanish.
msowww.anu.edu.au

LookWAYup English - Spanish Dictionary
Bidirectional English to Spanish dictionary, with definitions and thesaurus. Corrects spelling including accents.
lookwayup.com