lifespan vs lifetime

lifespan and lifetime both are nouns.

Word	Noun	Adjective	Verb	Adverb
lifespan	Yes	No	No	No
lifetime	Yes	No	No	No

As nouns, lifespan and lifetime are synonyms defined as:

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

Other synonyms of lifespan include life-time, life.

lifespan (noun)	lifetime (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)