WordNet

WordNet screenshots

In WordNet nouns, verbs, adjectives are grouped into sets of cognitive synonyms
Working Menu
WordNet 2.1 : Working Menu

Alternative downloads

TildeTech Dictionaries
The Dictionaries kit is optional and contains additional game dictionaries.
7.3.3870
FREE
Word Magic Pro Translation/Grammar & Syntax Pack
It has a translator suitable for school texts, memos, notices.
Word Magic Dictionary & Tools Home Edition
This is a Mega Dictionary with translations, idioms, synonyms, etc.
6.3.0.1017