1. Zoology. A respiratory aperture, especially:
   1. Any of several tracheal openings in the exoskeleton of an insect or a spider.
   2. A small respiratory opening behind the eye of certain fishes, such as sharks, rays, and skates.
   3. The blowhole of a cetacean.
2. An aperture or opening through which air is admitted and expelled.

[Middle English, from Latin spīrāculum, from spīrāre, to breathe.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.