Gehenna vs Inferno

Gehenna and Inferno both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gehenna	Yes	No	No	No
Inferno	Yes	No	No	No

As nouns, Inferno is a hypernym of Gehenna; that is, Inferno is a word with a broader meaning than Gehenna:

Gehenna: a place where the wicked are punished after death
Inferno: (Christianity) the abode of Satan and the forces of evil; where sinners suffer eternal punishment

Other hypernyms of Gehenna include Hell, infernal region, nether region, perdition, pit.

Gehenna (noun)	Inferno (noun)
a place where the wicked are punished after death	(Christianity) the abode of Satan and the forces of evil; where sinners suffer eternal punishment