slit vs fissure

slit and fissure both are nouns.

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

As nouns, fissure is a hypernym of slit; that is, fissure is a word with a broader meaning than slit:

Other hypernyms of slit include cleft, crack, crevice, scissure.

slit (noun)	fissure (noun)
a long narrow opening	(anatomy) a long narrow slit or groove that divides an organ into lobes
obscene terms for female genitals	a long narrow cleft
a narrow fissure	a long narrow depression in a surface
a depression scratched or carved into a surface

slit (verb)	fissure (verb)
cut a slit into	break into fissures or fine cracks
make a clean cut through