<p><strong>Noun:</strong></p><ul><li>an air or gas vent, especially one to carry off fumes from a tunnel, underground passage, etc.</li><li>either of two nostrils or spiracles, or a single one, at the top of the head in whales and other cetaceans, through which they breathe.</li><li>a hole in the ice to which whales or seals come to breathe.</li><li>Metallurgy: a defect in a casting or ingot caused by the escape of gas.</li><li>Geology: a hole in a sea cliff or coastal terrace through which columns of spray are jetted upward.</li></ul>