(Anat.) The nostril, or one of the nostrils, of whales, porpoises, and allied animals.
2.
(Zool.)
(a)
One of the external openings communicating with the air tubes or tracheae of insects, myriapods, and arachnids. They are variable in number, and are usually situated on the sides of the thorax and abdomen, a pair to a segment. These openings are usually elliptical, and capable of being closed.
(a)
A tubular orifice communicating with the gill cavity of certain ganoid and all elasmobranch fishes. It is the modified first gill cleft.
3.
Any small aperture or vent for air or other fluid.
... in the form of a circle; it is not girt with walls, but stands upon thick columns, beautifully grouped. A very large dome, built with great care in the centre or pole, contains another small vault as it were rising out of it, and in this is a spiracle, which is right over the altar. There is but one altar in the middle of the temple, and this is hedged round by columns. The temple itself is on a space of more than 350 paces. Without it, arches measuring about eight paces extend ... — The City of the Sun • Tommaso Campanells
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