The Collaborative International Dictionary of English v.0.48:

Stearin \Ste"a*rin\ (st[=e]"[.a]*r[i^]n), n. [Gr. ste`ar tallow,
   suet: cf. F. st['e]arine.] (Physiol. Chem.)
   One of the constituents of animal fats and also of some
   vegetable fats, as the butter of cacao. It is especially
   characterized by its solidity, so that when present in
   considerable quantity it materially increases the hardness,
   or raises the melting point, of the fat, as in mutton tallow.
   Chemically, it is a compound of glyceryl with three molecules
   of stearic acid, and hence is technically called tristearin,
   or glyceryl tristearate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stearin
    n 1: an ester of glycerol and stearic acid