Morphophonemic change has to do with the way the pronunciation of a morpheme changes in different contexts. Another way of saying it is that there is a change of one or more of the phonemes that make up the morpheme -- thus the term morphophonemic.
A morpheme is the the smallest part of a spoken word that contributes meaning to the word. Usually a given morpheme is pronounced the same in all contexts -- for instance, cat is always pronounced /kat/. But consider a noun like combine: I would analyse it into two morphemes: /kom/ and /bi n/ -- that is, the prefix com- and the base bine. But when we use combine as a verb, the stress shifts from the first to the second syllable, and this stress-shift changes the pronunciation of the vowel in the prefix: In the verb the <o> in the prefix reduces to a schwa sound:
/km/. That change of the vowel phoneme /o/ to schwa is a morphophonemic change: a change of phonemes within a single morpheme.
Combine also illustrates morphophonemic change in its base morpheme: If to the verb combine we add the suffix
-ation to form a noun, the vowel in the base undergoes a morphophonemic change. In the verb the base is pronounced /bi n/, with a long <i>, but in the noun combination the stress-shift again reduces the vowel in the base morpheme to a schwa.
There are other examples of morphophonemic change in the answer to the earlier question about morphophonemic writing . Click on “View all answers” and then Ctrl-F to “morphophonemic.”