Morph

Morph is a term which refers to alternative forms or realizations of a single morpheme.

Example
the English plural suffix is found in precisely three different pronounciations, /s/, /z/, and /@z/: cats /kats/, dogs /dogz/, and horses /ho:s@z/. Since these three elements all represent a single morpheme, they are called morphs, and we say that /s/, /z/, and /@z/ are allomorphs of the abstract or underspecified plural suffix /-Z/.

Links
Utrecht Lexicon of Linguistics