life-time vs lifespan

life-time and lifespan both are nouns.

Word	Noun	Adjective	Verb	Adverb
life-time	Yes	No	No	No
lifespan	Yes	No	No	No

As nouns, life-time and lifespan are synonyms defined as:

life-time and lifespan: the period during which something is functional (as between birth and death)

Other synonyms of life-time include life, lifetime.

life-time (noun)	lifespan (noun)
the period during which something is functional (as between birth and death)	the period during which something is functional (as between birth and death)