A variant pronunciation of a morpheme, especially when it involves a change of phonemes. Allomorphs which are phonologically related provide cases of phonological alternation, which can be important evidence as a part of phonological analysis. Allomorphs which do not have a phonological relationship are termed suppletive. For example, the English negative prefix "in-" of words like "in-tolerable" or "in-admissible" has the variant form (allomorph) "im-", which appears in such forms as "im-possible".