The Collaborative International Dictionary of English v.0.48:

Isomere \I"so*mere\, n. [Iso- + -mere.] (Zool.)
   1. A homologous or corresponding part or segment.
      [Webster 1913 Suppl.]

   2. (Chem.) same as Isomer. [archaic]
      [Webster 1913 Suppl. +PJC]