falling out vs rift

falling out and rift both are nouns.

Word	Noun	Adjective	Verb	Adverb
falling out	Yes	No	No	No
rift	Yes	No	No	No

As nouns, falling out and rift are synonyms defined as:

falling out and rift: a personal or social separation (as between opposing factions)

Other synonyms of falling out include breach, break, rupture, severance.

falling out (noun)	rift (noun)
a personal or social separation (as between opposing factions)	a personal or social separation (as between opposing factions)
	a narrow fissure in rock
	a gap between cloud masses