Definition & Meaning of "thesaurus"

What is a "thesaurus"?

A thesaurus is a reference book that provides lists of synonyms and antonyms for words. Unlike a dictionary, which defines words, a thesaurus helps users find alternative words with similar meanings or opposite meanings. It is useful for expanding vocabulary, avoiding repetition, and finding the most precise word to express a particular idea. A thesaurus organizes words according to their meanings, often grouping synonyms and antonyms together.