fissure vs volcano

fissure and volcano both are nouns.

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

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

fissure: a long narrow cleft
volcano: a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt

fissure (noun)	volcano (noun)
(anatomy) a long narrow slit or groove that divides an organ into lobes	a mountain formed by volcanic material
a long narrow cleft	a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt
a long narrow depression in a surface

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