(1):
(n.) A nostril or spiracle in the top of the head of a whale or other cetacean.
(2):
(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.
(3):
(n.) An air hole in a casting.
(4):
(n.) A hole in the ice to which whales, seals, etc., come to breathe.