The Collaborative International Dictionary of English v.0.48:

macabre \macabre\ (m[.a]*k[aum]"b[~e]r) adj.
   1. portraying human injury or death in a way so as to
      inspiring shock or horror; gruesome; ghastly; as, macabre
      tortures conceived by madmen. [Also spelled macaber.]

   Syn: ghastly, grisly, gruesome, lurid.
        [WordNet 1.5]

   2. Pertaining to or portraying the grim aspects of death, or
      the allegorical dance of death.
      [PJC]

WordNet (r) 3.0 (2006):

macabre
    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:

59 Moby Thesaurus words for "macabre":
   appalling, astounding, awe-inspiring, awesome, awful, blue,
   cadaverous, corpselike, deadly, deathlike, deathly, deathly pale,
   dire, direful, dread, dreaded, dreadful, eerie, eldritch, fearsome,
   fell, fiendish, formidable, frightening, frightful, ghastly,
   ghostlike, ghostly, ghoulish, gory, grim, grisly, grotesque,
   gruesome, haggard, hideous, horrendous, horrible, horrid, horrific,
   horrifying, livid, lurid, morbid, mortuary, pale, redoubtable,
   schrecklich, shocking, spookish, spooky, terrible, terrific,
   terrifying, tremendous, uncanny, unearthly, wan, weird