demoniacal vs demoniac

demoniacal is not a noun while demoniac is a noun.

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

As adjectives, demoniacal and demoniac are synonyms defined as:

demoniacal and demoniac: of, pertaining to, or like a demon or possession by a demon

Other synonyms of demoniacal include possessed.

demoniacal (noun)	demoniac (noun)
	someone who acts as if possessed by a demon

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