cranberry morphemes

“In linguistic morphology, a cranberry morpheme (or fossilized term) is a type of bound morpheme that cannot be assigned an independent meaning or grammatical function, but nonetheless serves to distinguish one word from another.”
So, given that the set of morphemes is a topologically closed set, we can riff off of the notion of independence (or lack thereof) to define its topological interior, namely, that its interior is comprised of the morphemes that have an independent meaning or grammatical function. Cranberry morphemes, then, comprise the topological boundary of the set of morphemes.

Here’s the rest of the Wikipedia article on this topic.

keywords: Linguistics, General Topology, Point-Set Topology, analogy