Cranberry morpheme

In morphology, a cranberry morpheme is a type of bound morpheme that cannot be assigned a meaning nor a grammatical function, but nonetheless serves to distinguish one word from the other.

Examples
The English word cranberry seems morphologically complex, since it must be distinguished from words such as raspberry, blackberry, and gooseberry. Still, cran has no meaning and does not function as an independent word: cranberry is the only word in which cran appears.

Comment
The existence of cranberry-morphemes plays a role in the discussion whether morphology is word based or morpheme based (e.g. Aronoff 1976).

Link
Utrecht Lexicon of Linguistics