Inferno vs Gehenna

Inferno and Gehenna both are nouns.

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

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

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

Other hyponyms of Inferno include Tartarus, hellfire, red region.

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