noun.
The act of breathing out; expulsion of air from the lungs in the process of respiration: opposed to inspiration.
noun.
The last emission of breath; cessation; death.
noun.
Close; end; conclusion; termination: as, the expiration of a month or year; the expiration of a contract or a lease.
noun.
That which is produced by audible expiring or breathing out, as a sound.
noun.
Emission of volatile matter from any substance; evaporation; exhalation: as, the expiration of oxygen by plants.