Definition of "thesaurus" in English

noun

1. A publication that provides synonyms (and sometimes antonyms and other semantic relations) for the words of a given language.

   • "Roget" is the leading brand name for a print English thesaurus that lists words under general concepts rather than just close synonyms.

2. (archaic) A dictionary or encyclopedia.

3. (information science) A hierarchy of subject headings: canonical titles of themes and topics, the titles serving as search keys.