Morpholexical rule

Morpholexical rule is a kind of lexical redundancy rule proposed by Lieber (1980) to relate allomorphs which are listed in the lexicon, to each other. Morpholexical rules apply in a subcomponent of the grammar which precedes both the word formation component proper and the phonological component. The main motivation for this type of rule is that there are cases in which word formation rules need to have access to derived allomorphs before the phonology applies.

Example
in the Australian language Warlbiri verbs have five conjugational classes, each taking a different set of allomorphs of tense suffixes. The present suffix has the allomorphs -nya, -nganya, -rninya, and -nanya. These forms are phonologically very similar, and it is tempting to derive them from a common underlying form by a kind of phonological rule. Warlbiri also has a rule of reduplication which basically says: copy the first two syllables or only the first if it has a long vowel. Given the fact that the suffix is either monosyllabic or bisyllabic, the precise shape of the allomorph must be known at the time the morphological rule of reduplication applies.

Links
Utrecht Lexicon of Linguistics