possessed vs demoniac

possessed is not a noun while demoniac is a noun.

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

As adjectives, possessed and demoniac are synonyms defined as:

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

Other synonyms of possessed include demoniacal.

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

possessed (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
influenced or controlled by a powerful force such as a strong emotion