allophone

from WordNet (r) 3.0 (2006)

allophone
    n 1: (linguistics) any of various acoustically different forms
         of the same phoneme

from The Collaborative International Dictionary of English v.0.48

allophone \allophone\ n.
   any one of two or more speech sounds that considered variants
   of the same phoneme. For example, the p sounds of pin and
   spin are allophones of p; and the t sounds of toe stop and
   catnip are allophones of t.
   [PJC]