noun (n)

• the spiracle of a cetacean located far back on the skull(noun.body)

  source: wordnet30
• a hole for the escape of gas or air(noun.artifact)

  Synonym:
  vent, vent-hole, venthole
  

  source: wordnet30
• 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.(noun)

  source: webster1913