Answer: blowhole

AnswerCrossword Clue
BLOWHOLEWhale's breather
BLOWHOLEMain opening?
blowholeA hole in ice to which seals, whales, and other aquatic animals come to breathe
blowholeA hole for blowing or breathing through, in particular
blowholeA vent for air or smoke in a tunnel or other structure
blowholean air or gas vent
blowholeA cavity in a metal casting, produced by the escape of air through the liquid metal
blowholeThe nostril of a whale on the top of its head