morphophoneme

:  a class of phonemes that belong to the same morpheme (as the \-s, -z, -ə̇z\ plural suffix of kits, kids, kisses; \f, v\ in knife, knives); also :  an arbitrarily selected member of such a class as its representative in grammatical description (as the plural suffix -s, or the f in \nīf\) group together into one morphophoneme the phonemes which replace each other in corresponding parts of the various members of a morpheme — Z. S. Harris