Blow"hole` (&?;), n. 1. A cavern in a cliff, at the water level, opening to the air at its farther extremity, so that the waters rush in with each surge and rise in a lofty jet from the extremity.

2. A nostril or spiracle in the top of the head of a whale or other cetacean.

&fist; There are two spiracles or blowholes in the common whales, but only one in sperm whales, porpoises, etc.

3. A hole in the ice to which whales, seals, etc., come to breathe.

4. (Founding) An air hole in a casting.

• The spiracle, on the top of the head, through which cetaceans breath
  
• A vent for the escape of gas
  
• A cavity in the ground that leads to a marine cave and out of which waves splash