thesaurus

US /θɪˈsɔːr.əs/
UK /θɪˈsɔːr.əs/
"thesaurus" picture
1.

a book or electronic resource that lists words in groups of synonyms and related concepts.

:
I used a thesaurus to find a better word for 'happy'.
A good writer often consults a thesaurus to enrich their vocabulary.