Is there such a thing as a mathematical thesaurus?
Solution 1:
There is a very comprehensive (at least very long!) "Handbook of Mathematical Discourse" which you can find here.
Under the various topics they list some synonyms, but I can't vouch for its completeness or accuracy. Also, it is more of a dictionary or encyclopedia than a pure thesaurus.
EDIT: Another question on Math.SE asks a similar question and one of the answers points to this online encyclopedia. It seems, however, that this one might be of limited use as a thesaurus. After a few tries it looks like synonyms are rarely included.