A prosthesis is an artificial body part that takes the place of a missing one: a leg, an arm, a tooth, sometimes a hand or an eye. Doctors fit it so a person can walk, hold things, chew, or look whole again. The plural is prostheses (the -is becomes -es). It is a hospital and clinic word; in everyday talk people often say “false leg,” “false teeth,” or “a prosthetic.” Though actually the idea is wider than legs — a dental prosthesis is a false tooth or a set of teeth. It is a stand-in for a real part, not a toy and not the same thing as the prostate.