expiration vs breath

expiration and breath both are nouns.

Word	Noun	Adjective	Verb	Adverb
expiration	Yes	No	No	No
breath	Yes	No	No	No

As nouns, breath is a hypernym of expiration; that is, breath is a word with a broader meaning than expiration:

expiration (noun)	breath (noun)
the act of expelling air from the lungs	the process of taking in and expelling air during breathing
euphemistic expressions for death	an indirect suggestion
a coming to an end of a contract period	a slight movement of the air
	the air that is inhaled and exhaled in respiration
	a short respite