[1] : The Collaborative International Dictionary of English v.0.48

fiendish \fiend"ish\, a.
   like a fiend; diabolically wicked or cruel; infernal;
   malignant; devilish; hellish. -- fiend"ishly, adv. --
   fiend"ishness, n.
   1913 webster
see also:
fiend"ishly fiend"ishness 

[2] : WordNet (r) 2.0

fiendish
     adj : 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, hellish, infernal, satanic,
            unholy
see also:
demonic diabolic diabolical hellish infernal satanic 
unholy 

[3] : Moby Thesaurus II by Grady Ward, 1.0

77 moby thesaurus words for "fiendish":
   draconian, mephistophelian, tartarean, animal, anthropophagous,
   atrocious, bad, baleful, barbaric, barbarous, beastly, bestial,
   bloodthirsty, bloody, bloody-minded, brutal, brutalized, brute,
   brutish, cannibalistic, cruel, cruel-hearted, cursed, damnable,
   demoniac, demoniacal, demonic, demonish, demonlike, devil-like,
   devilish, diabolic, diabolical, evil, execrable, fell, feral,
   ferocious, fiendlike, fierce, ghoulish, heinous, hellborn, hellish,
   infernal, inhuman, inhumane, malefic, maleficent, malevolent,
   malicious, malign, malignant, monstrous, murderous, ogreish,
   outrageous, ruthless, sadistic, sanguinary, sanguineous, satanic,
   savage, serpentine, sharkish, sinister, slavering, subhuman,
   truculent, unchristian, uncivilized, ungodly, unhallowed, unhuman,
   vicious, wicked, wolfish

Fiendish >> F Words
Fiendish, definition of term: Fiendish
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