ETYM Old Eng. nosethril, nosethirl, AS. nospyrl; nos for nosu nose + pyrel opening, hole, from pyrel pierced, for pyrhel, from purh through.
In vertebrates, the opening of the nasal cavity, in which cells sensitive to smell are located. (In fish, these cells detect water-borne chemicals, so they are effectively organs of taste.) In vertebrates with lungs, the nostrils also take in air. In humans, and most other mammals, the nostrils are located on the nose.
One of the external openings of the nose, which give passage to the air breathed and to secretions from the nose and eyes.