The Collaborative International Dictionary of English v.0.48:

Allelomorph \Al*le"lo*morph\, n. [Gr. ? of one another + Gr.
   morfh` form.] (Biol.)
   One of the pure unit characters commonly existing singly or
   in pairs in the germ cells of Mendelian hybrids, and
   exhibited in varying proportion among the organisms
   themselves; same as allele, 2. Allelomorphs which under
   certain circumstances are themselves compound are called
   hypallelomorphs. See Mendel's law. --
   Al*le`lo*mor"phic, a.
   [1913 Webster]

         As we know that the several unit characters are of such
         a nature that any one of them is capable of
         independently displacing or being displaced by one or
         more alternative characters taken singly, we may
         recognize this fact by naming such characters
         allelomorphs.                            --Bateson.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

allelomorph
    n 1: (genetics) either of a pair (or series) of alternative
         forms of a gene that can occupy the same locus on a
         particular chromosome and that control the same character;
         "some alleles are dominant over others" [syn: allele,
         allelomorph]