allomorph
Concise Oxford English Dictionary © 2008 Oxford University Press:
allomorph /ˈaləmɔːf/
▶noun Linguistics any of two or more representations of a morpheme, such as the plural endings /s/ (as in bats) and /z/ (as in bugs).
– derivatives
allomorphic adjective.
allomorphic adjective.
'allomorph' also found in these Oxford entries:

