WordWeb is a quick and powerful English thesaurus and dictionary for Windows. It can be used to lookup words from almost any Windows program, showing definitions, synonyms and related words. You can search for words matching a pattern, find and solve anagrams, and optionally search a large number of extra word lists.

Unlike any paper dictionary or thesaurus WordWeb is truly a Word Web - each set of synonyms is linked to other related sets. Lookup "tree", click on the "Types" tab and you'll have a list of different types of tree. Click on "Part of" and WordWeb will tell you that a tree can be part of a "forest" or "wood".