Affix substitution

Affix substitution is a type of morphological operation by which one affix takes the structural position of another affix. As a consequence of this operation, the two affixes in question cannot co-occur. Affix substitution is an alternative to truncation.

Example
The English suffix -ee attaches to transitive verbs (employ:employee, pay:payee). Although pairs such as nomin+ate:nomin+ee, evacu+ate:evacu+ee are semantically related, the nouns ending in -ee lack the verbal suffix -ate, and if it is assumed that word formation rules can only take words as their base these forms are problematic.

Comments
Some linguists have solved this problem by allowing for truncation rules, which delete a morpheme (in our example -ate) which is internal to an affix (in our example -ee) (cf. Aronoff, 1976). Others have tackled this problem by allowing for affix substitution: -ee takes the structural position of -ate, or, by the same token, -ate takes the position of -ee.

Link
Utrecht Lexicon of Linguistics