The Collaborative International Dictionary of English v.0.48:

Oleomargarine \O`le*o*mar"ga*rine\, n. [L. oleum oil + E.
   margarine, margarin.] [Written also oleomargarin.]
   1. A liquid oil made from animal fats (esp. beef fat) by
      separating the greater portion of the solid fat or
      stearin, by crystallization. It is mainly a mixture of
      olein and palmitin with some little stearin. [archaic]
      [1913 Webster]

   2. An artificial butter made by emulsifying a fatty oil with
      more or less milk and water; it was formerly made
      predominantly from animal fats, but now is made
      predominantly or exclusively from vegetable oils,
      sometimes mixed with animal fats.
      [1913 Webster +PJC]

   Note: Oleomargarine was wrongly so named, as it contains no
         margarin proper, but olein, palmitin, and stearin, a
         mixture of palmitin and stearin having formerly been
         called margarin by mistake.
         [1913 Webster]