The Collaborative International Dictionary of English v.0.48:

Santonin \San"to*nin\, n. [L. herba santonica, a kind of plant,
   fr. Santoni a people of Aquitania; cf. Gr. ?: cf. F.
   santonine.] (Chem.)
   A white crystalline substance having a bitter taste,
   extracted from the buds of levant wormseed and used as an
   anthelmintic. It occassions a peculiar temporary color
   blindness, causing objects to appear as if seen through a
   yellow glass.
   [1913 Webster]