nostril
n. countablen. one of the two holes in your nose that let air in and out. You have one on the left and one on the right.
n. one of the two external openings of the nose, through which air enters and exits the respiratory system. Often used in the plural to refer to the nose as a whole.
He held his breath and closed one nostril.
The cold wind stung her nostrils as she walked through the open field.
The horse's nostrils flared wide in response to the scent of the approaching predator, signaling a heightened state of alertness to the rest of the herd.
From Middle English nostrille, from Old English nosþyrel. Compare Old Frisian nosterle (“nostril”), modern West Frisian noaster (“nostrill”). Compare also Middle Low German noster (“nostril”), from Proto-Germanic *nustriz (“nostril”). By surface analysis, nose + thirl (“hole”).