Yes! There is a Thesaurus in Google Docs!

It is amazing how many Google Doc users overlook the thesaurus. The thesaurus is located within the define tool. When the define tool is used it opens a research window with a dictionary. The definitions are followed by a list of synonyms. Some of the definitions listed even include a listing of antonyms.

All you have to do to access the define tool is go to the tools heading and click on define.  Another way to open the dictionary is by right clicking on a highlighted word and then click on define.
Thesaurus Updates