The Collaborative International Dictionary of English v.0.48:

Tristearin \Tri*ste"a*rin\, n. [Pref. tri- + stearin.] (Physiol.
   Chem.)
   See Stearin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tristearin
    n 1: a triglyceride of stearic acid [syn: tristearin,
         glycerol tristearate]