blowhole

noun

1. The spiracle, on the top of the head, through which cetaceans breathe.
2. A hole in sea ice where cetaceans and pinnipeds come to breathe.
3. A top-facing opening to a cavity in the ground very near an ocean's shore, leading to a marine cave from which wave water or bursts of air are expelled.
4. A vent for the escape of steam or other gas.
5. An unintended cavity filled with air in a casting product.
6. A vertical opening in the top of a computer case that lets hot air (primarily from the CPU heat sink) escape quickly.

verb

1. (ambitransitive)To fill or be filled with air in an unintended cavity.