Definition - An affix that is placed within a morpheme.

1. In contrast to interfixes, which are placed between two morphemes to form a word.

Example -
One of the few English infixes is -ma-, which is used jocularly to give words false-sophistication, as in sophistimacated and edumacated.

Oxford English Dictionary -
The term's first citation is from 1881:
"The arguments establishing the … connection of the Cambojan and Malayan languages … based on the principle of modifying infixes."
(Nature XXIII. 271/1)

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