The Collaborative International Dictionary of English v.0.48:

Grewsome \Grew"some\, Gruesome \Grue"some\, a. [From a word akin
   to Dan. gru horror, terror + -some; cf. D. gruwzaam, G.
   grausam. Cf. Grisly.]
   Ugly; frightful.
   [1913 Webster]

         Grewsome sights of war.                  --C. Kingsley.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

gruesome \grue"some\, a.
   Ugly; frightful. Same as grewsome. [Scot.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

gruesome
    adj 1: shockingly repellent; inspiring horror; "ghastly wounds";
           "the grim aftermath of the bombing"; "the grim task of
           burying the victims"; "a grisly murder"; "gruesome
           evidence of human sacrifice"; "macabre tales of war and
           plague in the Middle ages"; "macabre tortures conceived
           by madmen" [syn: ghastly, grim, grisly, gruesome,
           macabre, sick]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "gruesome":
   abominable, appalling, astounding, awe-inspiring, awesome, awful,
   baleful, blue, cadaverous, corpselike, daunting, deadly, deathlike,
   deathly, deathly pale, dire, direful, dread, dreaded, dreadful,
   eerie, fearsome, fell, forbidding, formidable, foul, frightening,
   frightful, ghastly, ghostlike, ghostly, ghoulish, grim, grisly,
   grotesque, haggard, hideous, horrendous, horrible, horrid,
   horrific, horrifying, livid, loathsome, lurid, macabre, morbid,
   mortuary, offensive, pale, redoubtable, repellent, repelling,
   repugnant, repulsive, revolting, schrecklich, shocking, sinister,
   terrible, terrific, terrifying, tremendous, uncanny, unearthly,
   wan, weird