In linguistic morphology a cranberry morpheme (also called unique morpheme or fossilized term) is a type of bound morpheme that cannot be assigned an independent meaning and grammatical function, but nonetheless serves to distinguish one word from another.
[1] The eponymous archetypal example is the cran of cranberry.
Unrelated to the homonym cran with the meaning "a case of herrings", this cran actually comes from crane (the bird), although the connection is not immediately evident.
Phonetically, the first morpheme of raspberry also counts as a cranberry morpheme, even though the word "rasp" does occur by itself.
Compare these with blackberry, which has two obvious unbound morphemes ("black" + "berry"), and to loganberry and boysenberry, both of which have first morphemes derived from surnames (James Harvey Logan and Rudolph Boysen, respectively).