agnus castus

from The Collaborative International Dictionary of English v.0.48

Agnus castus \Ag"nus cas"tus\ [Gr. ? a willowlike tree, used at
   a religious festival; confused with ? holy, chaste.] (Bot.)
   A species of {Vitex} ({Vitex agnus castus}); the chaste tree.
   --Loudon.
   [1913 Webster]

         And wreaths of agnus castus others bore. --Dryden.
   [1913 Webster]