名詞 demoniac:

1. someone who acts as if possessed by a demon

形容詞 demoniac:

1. in a murderous frenzy as if possessed by a demon
   同義詞：amuck, amok, berserk, demoniacal, possessed
2. resembling or suggesting possession by a demon
   同義詞：demoniacal

de.mo.ni.ac

adj.（形容詞）
Possessed, produced, or influenced by a demon:
魔鬼的：被魔鬼占有、創(chuàng)造或影響的：
例句：
demoniac creatures.
受魔鬼控制的生物

Of, resembling, or suggestive of a devil; fiendish:
惡魔般的：惡魔一般，象惡魔一般的；魔鬼似的：
例句：
demoniac energy; a demoniacal fit.
魔鬼般的力量；極其合身

n.（名詞）
One who is or seems to be possessed by a demon.
著魔的人：被（或看上去象被）魔鬼控制的人

來源：
Middle English demoniak
中古英語 demoniak
from Late Latin daemoniacus
源自 后期拉丁語 daemoniacus
from Greek *daimoniakos
源自 希臘語 *daimoniakos
from daimonios [of a spirit]
源自 daimonios [神靈的]
from daimôn [divine power] * see demon
源自 daimôn [神的力量] *參見 demon

【引伸】
de.moni.acally
adv.（副詞）