blowhole

noun

1. an air or gas vent, especially one to carry off fumes from a tunnel, underground passage, etc.
2. either of two nostrils or spiracles, or a single one, at the top of the head in whales and other cetaceans, through which they breathe.
3. a hole in the ice to which whales or seals come to breathe.
4. Metallurgy. a defect in a casting or ingot caused by the escape of gas.
5. Geology. a hole in a sea cliff or coastal terrace through which columns of spray are jetted upward.

noun

1. the nostril, paired or single, of whales, situated far back on the skull
2. a hole in ice through which whales, seals, etc, breathe
3. 1. a vent for air or gas, esp to release fumes from a tunnel, passage, etc
   2. NZa hole emitting gas or steam in a volcanic region
4. a bubble-like defect in an ingot resulting from gas being trapped during solidification
5. geology a hole in a cliff top leading to a sea cave through which air is forced by the action of the sea