A reference book that contains synonyms and antonyms is called a thesaurus.
A thesaurus is a valuable resource for writers, students, and anyone looking to expand their vocabulary. Unlike a dictionary, which provides definitions of words, a thesaurus groups words based on similarities in meaning (synonyms) and opposites (antonyms). By using a thesaurus, you can find alternative words to express your ideas more vividly or to avoid repetition in your writing. Popular thesaurus titles include Roget’s Thesaurus and The Oxford Thesaurus, among others. Whether you’re crafting an essay, preparing a speech, or simply trying to enhance your language skills, a thesaurus is an essential tool to have at your disposal.