WordWeb Free Version

Look up a word in any program by holding down the Ctrl key and right-clicking on a word with the mouse. Alternatively you can press Ctrl+Alt+W.

WordWeb is a free English thesaurus and dictionary for Windows, and can be used to look up words from within almost any program in just one click. It works off-line, but can also look up words in web references such as the Wikipedia encyclopedia. Features of the free version include:
Definitions and synonyms
Proper nouns
Related words
Pronunciations
150 000 root words - 120 000 synonym sets
Look up words in almost any program
http://wordweb.info/free/

Auch diesen Tipp verdanke ich Christian Saling (siehe nachstehendes Posting)