I'd assume from the earlier meaning of "thesaurus" which comes from "treasury," or as it exists in my mind, treasure chest. > The meaning "encyclopedia filled

I'd assume from the earlier meaning of "thesaurus" which comes from "treasury," or as it exists in my mind, treasure chest. > The meaning "encyclopedia filled with information" is from 1840, but it existed earlier as thesaurarie (1590s), used as a title by some early dictionary compilers, on the notion of thesaurus verborum "a treasury of words." The meaning "collection of words arranged according to sense" is attested from 1852 in Roget's title. from: https://www.etymonline.com/word/thesaurus https://www.etymonline.com/word/thesaurus