\Spir"a*cle\, n.[L. spiraculum, fr. spirare to breathe:
cf. F. spiracule. See {Spirit}.]
1. (Anat.) The nostril, or one of the nostrils, of whales,
   porpoises, and allied animals.

2. (Zo["o]l.)
   (a) One of the external openings communicating with the
       air tubes or trache[ae] 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. See
       Illust. under {Coleoptera}.
   (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.