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

CAS General Subject Vocabulary Helper
Extensive listings for chemistry. Produced by Chemical Abstracts Service, a division of the American Chemical Society.

Maths Thesaurus
Definitions of common mathematical terms, along with broader, narrower, and related concepts.

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

Art and Architecture Thesaurus
Getty's terms, as used in several AAT indexes.

Eurodic Autom
European Union terminology. Available on most European Union languages.

Getty Thesaurus of Geographic Names
Structured vocabulary of place names.

Library of Congress Thesauri
Links to multiple LOC thesauri, including GLIN, the Global Legal Information Network.

Library of Congress Classification Schedules
A comprehensive list of LOC Classification schedules.

Alcohol and Other Drug Thesaurus - AOD
National Institutes of Health thesaurus. Provides resource for medical, social, and demographic terms related to alcohol and drug use.

ASIS Thesaurus of Information Science
Hierarchical and alphabetical interface to library-related terms.

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

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

Thesaurus of Musical Instruments
Over a thousand instruments, with relational links based on the Library of Congress Subject Headings.