nos ‧ tril /ˈnɒstrəl, ˈnɒstrɪl $ ˈnɑː-/ BrE AmE noun [countable]
[ Language: Old English ; Origin: nosthyrl 'nose-hole' ]
one of the two holes at the end of your nose, through which you breathe and smell things:
The smell of gunpowder filled his nostrils.
the horse’s flaring nostrils (=widened nostrils)