1. 
[syn: demonic, diabolic, diabolical, fiendish, hellish, infernal, satanic, unholy]
The Collaborative International Dictionary of English v.0.48:
Demonic \De*mo"nic\, a. [L. daemonicus, Gr. daimoniko`s.]
   Of or pertaining to a demon or to demons; demoniac. "Demonic
   ambushes." --Lowell.
   [1913 Webster]
WordNet (r) 3.0 (2006):
demonic
    adj 1: extremely evil or cruel; expressive of cruelty or
           befitting hell; "something demonic in him--something that
           could be cruel"; "fires lit up a diabolic scene";
           "diabolical sorcerers under the influence of devils"; "a
           fiendish despot"; "hellish torture"; "infernal
           instruments of war"; "satanic cruelty"; "unholy grimaces"
           [syn: demonic, diabolic, diabolical, fiendish,
           hellish, infernal, satanic, unholy]