| Definition -
1. A type of affix that consists of suprasegmental features, e.g. a stress or tone pattern.
2. A type of phonemeaffix where a change of tone or stress modifies an existing word's meaning. For example, the creation of nouns by changing the pronunciation of an existing word: the noun próduce (vegetables or fruit) was coined as an initially stressed version of the verb prodúce (create or bring forth).
Oxford English Dictionary - Its first citation is from 1951:
"Suprasegmental morphemes consisting of patterns of stress, with the possibility of including plus junctures, are called superfixes. Those consisting of pitches and a terminal juncture are called intonation patterns.…."
(Trager & Smith Outl. Eng. Structure ii. 56)
1. The OED now cites an even earlier instance, a paper by Trager in IJAL 1948
(mugdan at uni-muenster.de)