A portmanteau morph is a morph which jointly represents the values of two grammatical categories which otherwise are each represented by a morph of their own. It thus occupies two adjacent slots of a template. is a standard example: French au, phonologically /o/, is a portmanteau morph.
| . | a. | à | la | mère |
| French | dat | def.f.sg | mother(f) | |
| to the mother | ||||
| b. | au | père | ||
| dat:def.m.sg | father(m) | |||
| to the father | ||||
The phenomenon is widespread in inflectional morphology. For example, in conjugation, the pronominal indexes for the subject and the object may generally occupy two separate slots, but may merge into one morph for certain values of the categories in question. In declension, number and case may generally occupy two adjacent slots, but may merge into one morph for certain cases.