n. 1. A human being possessed by a demon or evil spirit; one whose faculties are directly controlled by a demon. [ 1913 Webster ]

The demoniac in the gospel was sometimes cast into the fire. Bates. [ 1913 Webster ]

2. (Eccl. Hist.) One of a sect of Anabaptists who maintain that the demons or devils will finally be saved. [ 1913 Webster ]

{ } a. [ L. daemoniacus, fr. daemon; cf. F. démoniaque. See Demon. ] 1. Pertaining to, or characteristic of, a demon or evil spirit; devilish; as, a demoniac being; demoniacal practices. [ 1913 Webster ]

Sarcastic, demoniacal laughter. Thackeray. [ 1913 Webster ]

2. Influenced or produced by a demon or evil spirit; as, demoniac or demoniacal power. “Demoniac frenzy.” Milton. [ 1913 Webster ]

3. resembling or suggesting possession by a demon; as, demoniac energy. [ WordNet 1.5 ]

4. in a murderous frenzy as if possessed by a demon.
Syn. -- amuck, amok, berserk, demoniac, possessed(predicate). [ WordNet 1.5 ]

adv. In a demoniacal manner. [ 1913 Webster ]

n. The state of being demoniac, or the practices of demoniacs. [ 1913 Webster ]