the ‧ sau ‧ rus /θɪˈsɔːrəs/ BrE AmE noun ( plural thesauruses or thesauri /-raɪ/) [countable]
[ Date: 1800-1900 ; Language: Latin ; Origin: 'treasure, collection' , from Greek thesauros ]
a book in which words are put into groups with other words that have similar meanings