1. A hole that allows the passage of air, a hole through which air may pass, as for breathing. air-hole
2. A local region of low pressure or descending air that causes a plane to lose height suddenly

The spiracle of a cetacean located far back on the skull.
1. A hole in metal caused by a bubble of gas captured during solidification
2. A nostril in the top of the head of a cetacean and especially a whale