geological fault vs fissure

geological fault and fissure both are nouns.

Word	Noun	Adjective	Verb	Adverb
geological fault	Yes	No	No	No
fissure	Yes	No	Yes	No

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

geological fault: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other
fissure: a long narrow cleft

Other hypernyms of geological fault include cleft, crack, crevice, scissure.

geological fault (noun)	fissure (noun)
(geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other	(anatomy) a long narrow slit or groove that divides an organ into lobes
	a long narrow cleft
	a long narrow depression in a surface

geological fault (verb)	fissure (verb)
	break into fissures or fine cracks