Pronunciation: (blō'hōl"),[key] —n. 1. an air or gas vent, esp. 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. Metall.a defect in a casting or ingot caused by the escape of gas.
5. Geol.a hole in a sea cliff or coastal terrace through which columns of spray are jetted upward.