thesaurus

Language reference book organized to help in finding words related to a core concept but having different shades of meaning (connotations). Unlike a dictionary (which is organized to help in finding the meaning if you know the word), a thesaurus requires you to know the intended meaning to help find the correct word. Unlike a dictionary of synonyms (which is an alphabetical list of related words) a thesaurus is structured around ideas, and serves as a treasury of knowledge. First English language thesaurus (the 'Roget's Thesaurus') was created in 1852 by the UK surgeon Dr. Peter Mark Roget (1779-1869). The term is derived from the Greek word 'thesauros,' treasure.