Mathematical Thesaurus Save
Defines mathematical words and concepts, and indicates the links between them.
http://thesaurus.maths.org/   

Phrase Finder Save
Enter a single word and it will return a list of phrases and sayings that are related to the word in some way.
http://www.phrases.org.uk/   

Roget's II - The New Thesaurus Save
Contains 35,000 synonyms, succinct word definitions and a hyperlinked category index.
http://www.bartleby.com/62/   

Roget's International Thesaurus of English Words and Phrases Save
85,000 hyperlinked cross-references, plus proverbs and quotations from classic and modern authors.
http://www.bartleby.com/110/   

Thesaurus.com Save
Searchable online version of Roget's Thesaurus of English words and phrases.
http://thesaurus.reference.com/   

WWWebster Thesaurus Save
Searchable online thesaurus from Merriam-Webster.
http://www.m-w.com/thesaurus.htm   

Wordsmyth Save
A dictionary and thesaurus in one. Also gives parts of speech and examples for more than 50,000 words.
http://www.wordsmyth.net/   

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