What is a synonym for thesaurus?

There isn't really a single perfect synonym for "thesaurus" as it's a unique word with a specific meaning. However, depending on the context, you could use:

General synonyms:

* Word list

* Dictionary of synonyms

* Synonym finder

* Glossary of synonyms

More specific synonyms:

* Lexicon (a dictionary of a language or a subject)

* Roget's Thesaurus (a specific type of thesaurus, often used as a general term)

* Synonym dictionary

The best synonym to use will depend on what you're trying to convey.