n.1. (used with a pl. verb) The changes in pronunciation undergone by allomorphs of morphemes as they are modified by neighboring sounds, as the plural allomorphs in cat-s, dog-s, box-es, or as they are modified for grammatical reasons in the course of inflection or derivation, as house versus to house and housing.
2. (used with a sing. verb) The study of the morphophonemics of a language.