Nostril

Definition
noun, plural: nostrils
The external opening of the nose, which serves as a passageway for air and other gases and for secretions from the nose.
Supplement
In most animals, the nostrils are in pairs. In sperm whales, porpoises and other related animals, there is only one nostril and it is located on top of their head (where it is called spiracle). In birds, the nostrils can be found on the beak. Fish do not breathe air through their noses. However, they have two small orifices for smelling, hence, may be referred to as nostrils. Humans have two external and two internal nostrils inside the head.
Word origin: Middle English nostrille, from Old English nosthyrl : nosu, nose.
Synonym:

• naris