The Collaborative International Dictionary of English v.0.48:

Salicin \Sal"i*cin\, n. [L. salix, -icis, a willow: cf. F.
   salicine. See Sallow the tree.] (Chem.)
   A glucoside found in the bark and leaves of several species
   of willow (Salix) and poplar, and extracted as a bitter
   white crystalline substance.
   [1913 Webster]