devil vs demoniac

devil and demoniac both are nouns.

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

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

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

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

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