Found:

allomorphy

MORPHOLOGY: the phenomenon that a single morpheme has different realizations, i.e. alternative forms depending on the phonological or morphological context in which it appears. In English, the plural suffix has three pronunciations: (a) /s/ after nouns ending in a voiceless consonant (cats /kats/), (b) /z/ after nouns ending in a voiced consonant (dogs /dogz/), and (c) /@z/ after nouns ending in a coronal sibilant (horses /hors@z/). In another type of allomorphy, the realization of a morpheme is conditioned by the presence of another morpheme. The English suffix -able is pronounced /@bl/ in adjectives such as possible and probable, but when the noun-forming suffix -ity is attached to it it is pronounced as /@bil/ (possibility, probability).

LIT.	Aronoff, M. (1976) Scalise, S. (1984) Spencer, A. (1991)