Webster's Revised Unabridged Dictionary · 1913

Demoniac

Demoniac , adjective

[Latin daemoniacus, from daemon; compare French démoniaque. See Demon.]

1.
Pertaining to, or characteristic of, a demon or evil spirit; devilish; as, a demoniac being; demoniacal practices.
Sarcastic, demoniacal laughter. — Thackeray
2.
Influenced or produced by a demon or evil spirit; as, demoniac or demoniacal power.
Demoniac frenzy. — Milton
3.
resembling or suggesting possession by a demon; as, demoniac energy.
4.
in a murderous frenzy as if possessed by a demon.

Also: Demoniacal

Demoniac , noun

1.
A human being possessed by a demon or evil spirit; one whose faculties are directly controlled by a demon.
The demoniac in the gospel was sometimes cast into the fire. — Bates
2.
(Ecclesiastical Hist.) One of a sect of Anabaptists who maintain that the demons or devils will finally be saved.