Source : Webster's Revised Unabridged Dictionary (1913)

Hellish \Hell"ish\, a.
   Of or pertaining to hell; like hell; infernal; malignant;
   wicked; detestable; diabolical. ``Hellish hate.'' --Milton.
   -- {Hell"ish*ly}, adv. -- {Hell"ish*ness}, n.

Source : WordNet®

hellish
     adj 1: very unpleasant; "hellish weather"; "stop that god-awful
            racket" [syn: {beastly}, {god-awful}]
     2: 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}, {infernal}, {satanic}, {unholy}]