demoniac vs demoniacal

demoniac is a noun but demoniacal is not a noun.

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

As adjectives, demoniac and demoniacal are synonyms defined as:

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

Other synonyms of demoniac include possessed.

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

demoniac (adjective)	demoniacal (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