thesauri

from The Collaborative International Dictionary of English v.0.48

Thesaurus \The*sau"rus\, n.; pl. {Thesauri}. [L. See
   {Treasure}.]
   A treasury or storehouse; hence, a repository, especially of
   knowledge; -- often applied to a comprehensive work, like a
   dictionary or cyclopedia.
   [1913 Webster]