separation vs rift

separation and rift both are nouns.

Word	Noun	Adjective	Verb	Adverb
separation	Yes	No	No	No
rift	Yes	No	No	No

As nouns, rift is a hyponym of separation; that is, rift is a word with a more specific, narrower meaning than separation:

Other hyponyms of separation include breach, break, falling out, rupture, severance, break.

separation (noun)	rift (noun)
the social act of separating or parting company	a personal or social separation (as between opposing factions)
the act of dividing or disconnecting	a narrow fissure in rock
(law) the cessation of cohabitation of man and wife (either by mutual agreement or under a court order)	a gap between cloud masses
sorting one thing from others
the distance between things
coming apart
the termination of employment (by resignation or dismissal)
the space where a division or parting occurs
the state of lacking unity