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.