Openings in the tops of whales' heads where they breathe, or any hole that allows air to escape or enter.
From 'blow' (air movement) + 'hole' (opening). Dating to the 1800s, 'blowhole' was first used to describe the breathing apertures of whales, then generalized to mean any vent or opening.
Whales have TWO blowholes that blow separately—left and right—allowing them to breathe while keeping one side of their brain awake while they sleep, which is one of nature's weirdest survival tricks!
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