Gehenna vs Hell

Gehenna and Hell both are nouns.

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

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

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

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

Gehenna (noun)	Hell (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
	(religion) the world of the dead