The Collaborative International Dictionary of English v.0.48:

Margarin \Mar"ga*rin\, n. [Cf. F. margarine. See Margarite.]
   (Physiol. Chem.)
   A fatty substance, extracted from animal fats and certain
   vegetable oils, formerly supposed to be a definite compound
   of glycerin and margaric acid, but now known to be simply a
   mixture or combination of tristearin and tripalmitin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

margarin
    n 1: a glyceryl ester of margaric acid [syn: margarin,
         glycerol trimargarate]
    2: a spread made chiefly from vegetable oils and used as a
       substitute for butter [syn: margarine, margarin, oleo,
       oleomargarine, marge]