demoniac /dɪˈməʊnɪak/adjective 2noun 1forms 3 adjective2 •Of or pertaining to demons; demonic.How dark may be the hiding of God's face, Or what demoniac forms may seize the helm Of reason... — 1827 •Possessed or controlled by a demon. noun1 •Someone who is possessed by a demon.The exorcism was dropped from the second Edwardian Prayer Book, because of its implication that unbaptised infants were demoniacs […]. — 1971 formsdemoniacs · more demoniac · most demoniac