A Thesaurus is a valuable tool for a writer. But look up the word Thesaurus in a Thesaurus and it is difficult to describe briefly. Yes it is an assembly of synonyms and antonyms but there is no other good single other word for the book. They toss around terms like “treasury of words” and “language reference book” but none has the panache of the book founded by Mr. Roget. However it is wise to use sparingly. It is not recommended to be overly ornamental in your use of synonyms when you have so many available. It can blunt the directness and power of your work.