The Collaborative International Dictionary of English v.0.48:

Quassin \Quas"sin\, n. [Cf. F. quassine. See Quassia.] (Chem.)
   The bitter principle of quassia, extracted as a white
   crystalline substance; -- formerly called quassite.
   [Written also quass[imac]in, and quassine.]
   [1913 Webster]