[ noun ] the hole where a key is inserted <noun.artifact>
Keyhole \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} (Zo["o]l.), 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} (Zo["o]l.), 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.
The gown also featured a sweetheart neckline with a keyhole opening in the back.
Convicts with long terms or dangerous records also wear "black boxes" over the chain linking their handcuffs to restrict lateral motion and cover the handcuffs' keyhole.