“polysemy: The property of a single word which has two or more distinct but related senses. Thus the noun screen is polysemous, since it is used variously of a fire screen, a cinema screen, a television screen, and so on.
Compare homonymy. The difference, in principle, is that in cases of homonymy the senses are quite unconnected; therefore they are not treated as belonging to the same word. But in many cases, it is hard to decide, and in theories of meaning the distinction is not always seen as valid.
Excerpted from: Matthews, P.H., ed. The Oxford Concise Dictionary of Linguistics. New York: Oxford University Press, 2014.