Key″hole′ (?), n. 1. A hole or apertupe in a door or lock, for receiving a key.
2. (a) (Carp.) A hole or excavation in beams intended to be joined together, to receive the key which fastens them. (b) (Mach.) a mortise for a key or cotter.
Keyhole limpet(Zoöl.), a marine gastropod of the genus Fissurella and allied genera. See Fissurella. — Keyhole saw, a narrow, slender saw, used in cutting keyholes, etc., as in doors; a kind of compass saw or fret saw. — Keyhole urchin(Zoöl.), any one of numerous clypeastroid sea urchins, of the genera Melitta, Rotula, and Encope; — so called because they have one or more perforations resembling keyholes.