Definition of thesaurus. 1a : a book of words or of information about a particular field or set of concepts especially : a book of words and their synonyms. b : a list of subject headings or descriptors usually with a cross-reference system for use in the organization of a collection of documents for reference and retrieval.What is a synonym in English?
Definition of synonym in English: synonym. noun. 1A word or phrase that means exactly or nearly the same as another word or phrase in the same language, for example shut is a synonym of close. 1.1 A person or thing so closely associated with a particular quality or idea that the mention of their name calls it to mind.