Etymology

The word "thesaurus" is derived from 16th-century New Latin, in turn from Latin thēsaurus, which is the latinisation of the Greek θησαυρός (thēsauros), literally "treasure store", generally meaning a collection of things which are of big importance or value (and thus the medieval rank of thesaurer was a synonym for treasurer). This meaning has been largely supplanted by Roget's usage of the term.