Mathematical Thesaurus [ Kids/Teens/Mature Teens ] - Defines mathematical words and concepts, and indicates the links between them.
Phrase Finder [ Kids/Teens/Mature Teens ] - Enter a single word and it will return a list of phrases and sayings that are related to the word in some way.
Roget's II - The New Thesaurus [ Teens/Mature Teens ] - Contains 35,000 synonyms, succinct word definitions and a hyperlinked category index.
