The Collaborative International Dictionary of English v.0.48:

Dismal \Dis"mal\, a. [Formerly a noun; e. g., "I trow it was in
   the dismalle." Chaucer. Of uncertain origin; but perh. (as
   suggested by Skeat) from OF. disme, F. d[^i]me, tithe, the
   phrase dismal day properly meaning, the day when tithes must
   be paid. See Dime.]
   1. Fatal; ill-omened; unlucky. [Obs.]
      [1913 Webster]

            An ugly fiend more foul than dismal day. --Spenser.
      [1913 Webster]

   2. Gloomy to the eye or ear; sorrowful and depressing to the
      feelings; foreboding; cheerless; dull; dreary; as, a
      dismal outlook; dismal stories; a dismal place.
      [1913 Webster]

            Full well the busy whisper, circling round,
            Convey'd the dismal tidings when he frowned.
                                                  --Goldsmith.
      [1913 Webster]

            A dismal description of an English November.
                                                  --Southey.

   Syn: Dreary; lonesome; gloomy; dark; ominous; ill-boding;
        fatal; doleful; lugubrious; funereal; dolorous;
        calamitous; sorrowful; sad; joyless; melancholy;
        unfortunate; unhappy.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dismal
    adj 1: causing dejection; "a blue day"; "the dark days of the
           war"; "a week of rainy depressing weather"; "a
           disconsolate winter landscape"; "the first dismal
           dispiriting days of November"; "a dark gloomy day"; "grim
           rainy weather" [syn: blue, dark, dingy,
           disconsolate, dismal, gloomy, grim, sorry,
           drab, drear, dreary]

Moby Thesaurus II by Grady Ward, 1.0:

205 Moby Thesaurus words for "dismal":
   Cassandra-like, Cassandran, Cassandrian, Quaker-colored, acier,
   affecting, afflictive, affording no hope, apathetic, arid, ashen,
   ashy, barren, bitter, black, blah, blank, bleak, bloodless, blue,
   canescent, characterless, cheerless, cinerary, cinereous, cinerous,
   cold, colorless, comfortless, cynical, dapple, dapple-gray,
   dappled, dappled-gray, dark, dead, defeatist, deplorable,
   depressing, depressive, despairing, desperate, despondent, dingy,
   dirgelike, discomforting, disconsolate, disheartening, dismaying,
   distressful, distressing, doleful, dolorific, dolorogenic,
   dolorous, dove-colored, dove-gray, downbeat, draggy, drear,
   drearisome, dreary, dry, dryasdust, dull, dusty, effete,
   elephantine, empty, epitaphic, etiolated, exequial, fade, feral,
   flat, forlorn, funebrial, funebrious, funebrous, funeral, funerary,
   funereal, glaucescent, glaucous, gloomy, grave, gray, gray-black,
   gray-brown, gray-colored, gray-drab, gray-green, gray-spotted,
   gray-toned, gray-white, grayed, grayish, grievous, grim, griseous,
   grizzle, grizzled, grizzly, heavy, ho-hum, hollow, hopeless,
   in despair, inane, inexcitable, insipid, iron-gray, jejune,
   joyless, lamentable, lead-gray, leaden, lifeless, livid,
   low-spirited, lowering, lugubrious, melancholy, miserable, morose,
   mortuary, mournful, mouse-colored, mouse-gray, mousy, moving,
   necrological, negative, negativistic, nihilistic, obituary,
   obsequial, oppressive, painful, pale, pallid, pathetic, pearl,
   pearl-gray, pearly, pedestrian, pessimist, pessimistic, piteous,
   pitiable, plodding, poignant, pointless, poky, ponderous,
   regrettable, rueful, sad, saddening, saturnine, sepulchral, sharp,
   silver, silver-gray, silvered, silvery, slate-colored, slaty, slow,
   smoke-gray, smoky, sober, solemn, somber, sombrous, sore,
   sorrowful, spiritless, steel-gray, steely, sterile, stiff, stodgy,
   stone-colored, stuffy, superficial, tasteless, taupe, tedious,
   touching, triste, uncheerful, uncomfortable, unhappy, unhopeful,
   unlively, vapid, weariful, wearisome, weary, without hope,
   woebegone, woeful, wooden, wretched