The nostril on top of a whale's or dolphin's head used for breathing, or an opening in rock through which sea spray is forced.
From 'blow' (Old English 'blawan', to wind) and 'hole' (Old English 'hol'). Whalers first documented this terminology in the 17th century.
Whale blowholes are actually their nostrils that migrated to the top of their heads over millions of years as they evolved from land mammals—you're looking at evolution's solution to going underwater while staying a mammal.
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