a breathing hole; an opening by which a confined space has communication with the outer air; air hole.

Zoology .

an aperture or orifice through which air or water passes in the act of respiration, as the blowhole of a cetacean.

an opening in the head of sharks and rays through which water is drawn and passed over gills.

one of the external orifices of the tracheal respiratory system of certain invertebrates, usually on the sides of the body.