WordWeb is a one-click English thesaurus and dictionary that can look up words in almost any program.

It works off-line, but can also look up words in web references such as the Wikipedia encyclopedia, web references, etc.

It is a free cut-down version of the Pro version. The comprehensive English thesaurus and dictionary has the folowing features:

Hundreds of thousands of definitions and synonyms
Related words
5,000 audio pronunciations
65,000 text pronunciations
150,000 root words
120,000 synonym sets
Look up words in almost any program
The latest international English words