The phenomenon that a word has several different meanings which are closely related to each other. The ambiguity of church (either a building or an institution) is an instance of polysemy.
The English word mouth refers first of all to the opening of the buccal cavity, but next to this it refers to the point where a river joins the sea.
Aronoff, M. 1976. Word Formation in Generative Grammar, MIT-press, Cambridge, Mass.
Spencer, A. 1991. Morphological Theory, Blackwell, Oxford.