A book containing a classified list of synonyms WordNet 3.0 & Open English WordNet

A thesaurus, sometimes called a synonym dictionary or dictionary of synonyms, is a reference work which arranges words by their meanings, sometimes as a hierarchy of broader and narrower terms, sometimes simply as lists of synonyms and antonyms. Wikipedia

Reference work that helps find words with similar meanings. Wikipedia Disambiguation

Work listing words grouped into categories in part topical and in part semantic, e.g. Roget's thesaurus Wikidata

A publication, usually in the form of a book, that provides synonyms (and sometimes antonyms) for the words of a given language. Wiktionary

Book of synonyms. Wiktionary (translation)