A hole or apertupe in a door or lock, for receiving a key. [1913 Webster]
A hole or excavation in beams intended to be joined together, to receive the key which fastens them. [1913 Webster]

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.

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OXFORD DICTIONARY

keyhole, n. a hole by which a key is put into a lock.

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THESAURUS

keyhole

air hole, armhole, blowhole, bullet-hole, bunghole, cringle, deadeye, eye, eyelet, gasket, grommet, guide, knothole, loop, loophole, manhole, mousehole, peephole, pigeonhole, pinhole, placket, placket hole, porthole, punch-hole, spiracle, tap, vent, venthole

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ROGET THESAURUS

keyhole

Opening

N opening, hole, foramen, puncture, perforation, fontanel, transforation, pinhole, keyhole, loophole, porthole, peephole, mousehole, pigeonhole, eye of a needle, eyelet, slot, opening, aperture, apertness, hiation, yawning, oscitancy, dehiscence, patefaction, pandiculation, chasm, embrasure, window, casement, abatjour, light, sky light, fan light, lattice, bay window, bow window, oriel, dormer, lantern, outlet, inlet, vent, vomitory, embouchure, orifice, mouth, sucker, muzzle, throat, gullet, weasand, wizen, nozzle, placket, portal, porch, gate, ostiary, postern, wicket, trapdoor, hatch, door, arcade, cellarway, driveway, gateway, doorway, hatchway, gangway, lich gate, way, path, thoroughfare, channel, passage, passageway, tube, pipe, water pipe, air pipe, vessel, tubule, canal, gut, fistula, adjutage, ajutage, ostium, smokestack, chimney, flue, tap, funnel, gully, tunnel, main, mine, pit, adit, shaft, gallery, alley, aisle, glade, vista, bore, caliber, pore, blind orifice, fulgurite, thundertube, porousness, porosity, sieve, cullender, colander, cribble, riddle, screen, honeycomb, apertion, perforation, piercing, terebration, empalement, pertusion, puncture, acupuncture, penetration, key, opener, master key, password, combination, passe- partout, open, perforated, perforate, wide open, ajar, unclosed, unstopped, oscitant, gaping, yawning, patent, tubular, cannular, fistulous, pervious, permeable, foraminous, vesicular, vasicular, porous, follicular, cribriform, honeycombed, infundibular, riddled, tubulous, tubulated, piped, tubate, opening, aperient, Int, open sesame!.

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