Nos"tril (?), n. [OE. nosethril, nosethirl, AS. nospyrl; nos for nosu nose + pyrel opening, hole, from pyrel pierced, for pyrhel, fr. purh through. ? See Nose, and Through, and cf. Thrill.]

1. (Anat.) One of the external openings of the nose, which give passage to the air breathed and to secretions from the nose and eyes; one of the anterior nares.

☞ In sperm whales, porpoises, and allied animals, there is only one nostril, which is situated on the top of the head and called a spiracle.

2. Perception; insight; acuteness. [Obs.]

Methinks a man
Of your sagacity and clear nostril should
Have made another choice.
B. Jonson.