[de.mo.ni.ac] also de.mo.ni.a.cal adj [ME demoniak, fr. LL daemoniacus, fr. Gk daimoniakos, fr. daimon-, daimon] (14c) 1: possessed or influenced by a demon
2: of, relating to, or suggestive of a demon: fiendish "~ cruelty" -- de.mo.ni.a.cal.ly adv
[2]demoniac n (14c): one possessed by a demon