departed vs infernal

departed and infernal both are nouns.

Word	Noun	Adjective	Verb	Adverb
departed	Yes	Yes	No	No
infernal	Yes	Yes	No	No

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

Other hyponyms of departed include living dead, zombi, zombie.

departed (noun)	infernal (noun)
someone who is no longer alive	an inhabitant of Hell

departed (adjective)	infernal (adjective)
dead	being of the underworld
well in the past; former	characteristic of or resembling Hell
	of or pertaining to or characteristic of a very uncontrolled and intense fire
	expletives used informally as intensifiers
	extremely evil or cruel; expressive of cruelty or befitting hell