blowhole

n. 1. 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. [ 1913 Webster ]

2. A nostril or spiracle in the top of the head of a whale or other cetacean. [ 1913 Webster ]

☞ There are two spiracles or blowholes in the common whales, but only one in sperm whales, porpoises, etc. [ 1913 Webster ]

3. A hole in the ice to which whales, seals, etc., come to breathe. [ 1913 Webster ]

4. (Founding) An air hole in a casting. [ 1913 Webster ]