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.
- An opening or one of a pair of openings for breathing, located on the top of the head of cetaceans, such as whales and dolphins. The blowhole is opened by muscles upon surfacing and closed by the pressure of water upon diving.
- A hole in ice to which aquatic mammals, such as dolphins, come to breathe.
- A vent to permit the escape of air or other gas.