portmanteau morph
Definition -
(1) A morpheme which simultaneously represents two other morphemes.
(2) The combining of two function words, e.g. the French au was coined from à le.

Etymology -
The term was probably modelled on portmanteau word.

Oxford English Dictionary -
Its first citation is from 1947:
"Some may…prefer to reinterpret portmanteaus as bimorphic as well as bimorphemic, even though to do so one must extend the definition of ‘morph’ to cover elements of other than overt phonemic content."
(Language XXIII. 339)

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