days vs life

days and life both are nouns.

Word	Noun	Adjective	Verb	Adverb
days	Yes	No	No	No
life	Yes	No	No	No

As nouns, life is a hypernym of days; that is, life is a word with a broader meaning than days:

days (noun)	life (noun)
the time during which someone's life continues	living things collectively
	animation and energy in action or expression
	the experience of being alive; the course of human events and activities
	an account of the series of events making up a person's life
	a motive for living
	a living person
	the organic phenomenon that distinguishes living organisms from nonliving ones
	the condition of living or the state of being alive
	a characteristic state or mode of living
	the course of existence of an individual; the actions and events that occur in living
	the period during which something is functional (as between birth and death)
	the period between birth and the present time
	the period from the present until death
	a prison term lasting as long as the prisoner lives