demoniac vs devil

demoniac and devil both are nouns.

Word	Noun	Adjective	Verb	Adverb
demoniac	Yes	Yes	No	No
devil	Yes	No	Yes	No

As nouns, devil is a hypernym of demoniac; that is, devil is a word with a broader meaning than demoniac:

Other hypernyms of demoniac include demon, fiend, monster, ogre.

demoniac (noun)	devil (noun)
someone who acts as if possessed by a demon	a word used in exclamations of confusion
	an evil supernatural being
	a cruel wicked and inhuman person
	a rowdy or mischievous person (usually a young man)

demoniac (adjective)	devil (adjective)
of, pertaining to, or like a demon or possession by a demon

demoniac (verb)	devil (verb)
	coat or stuff with a spicy paste
	cause annoyance in; disturb, especially by minor irritations