fissure vs rift

fissure and rift both are nouns.

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

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

fissure (noun)	rift (noun)
(anatomy) a long narrow slit or groove that divides an organ into lobes	a personal or social separation (as between opposing factions)
a long narrow cleft	a narrow fissure in rock
a long narrow depression in a surface	a gap between cloud masses

fissure (verb)	rift (verb)
break into fissures or fine cracks