thesaurus

Etymology

16th century, from Latin thēsaurus, from Ancient Greek θησαυρός (thēsaurós, “storehouse, treasure”); its current English usage/meaning was established soon after the publication of Peter Roget's Thesaurus of English Words and Phrases in 1852. Doublet of treasure.

noun

1. A publication, traditionally in the form of a book and now often online, 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 — canonic titles of themes and topics, the titles serving as search keys.