A natural opening or perforation through a bone or a membranous structure.

synonym: hiatus.

Roget 260: 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 etc. (interval) 198.    embrasure, window, casement; abatjour^†; light; sky light, fan light; lattice; bay window, bow window; oriel [Arch.]; 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 etc. 627; thoroughfare; channel; passage, passageway; tube, pipe; water pipe etc. 350; air pipe etc. 351; 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 etc. v.; terebration^†, empalement^†, pertusion^†, puncture, acupuncture, penetration.    key etc. 631, opener, master key, password, combination, passe-partout.    ... show more