\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.

Note: 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.