1. (n.) A cavern in a cliff, at the water level, opening to the air at its farther extremity, so that the waters rush in with each surge and rise in a lofty jet from the extremity.

2. (n.) A nostril or spiracle in the top of the head of a whale or other cetacean.

3. (n.) A hole in the ice to which whales, seals, etc., come to breathe.

4. (n.) An air hole in a casting.

air duct air hole air passage air shaft air tube airway armhole avenue breathing hole bullet-hole bunghole channel chute cringle deadeye debouch door egress emunctory escape estuary exhaust exit eye eyelet floodgate flume gasket grommet guide keyhole knothole loop loophole louver louverwork manhole mousehole naris nostril opening out outcome outfall outgate outgo outlet peephole pigeonhole pinhole placket placket hole pore port porthole punch-hole sally port shaft sluice spilehole spiracle spout tap touchhole transom vent ventage venthole ventiduct ventilating shaft ventilator vomitory way out weir wind tunnel