WordWeb is truly a Word Web - each set of synonyms is linked to other related sets. Look up "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".

WordWeb is a comprehensive one-click English thesaurus and dictionary for Windows. It can be used to look up words from almost any program, showing definitions, synonyms and related words. It includes pronunciations and usage examples, and has helpful spelling and sounds-like links. Learn more.