The Collaborative International Dictionary of English v.0.48:

Mealy \Meal"y\ (m[=e]l"[y^]), a. [Compar. Mealier; superl.
   Mealiest.]
   1. Having the qualities of meal; resembling meal; soft, dry,
      and friable; easily reduced to a condition resembling
      meal; as, a mealy potato.
      [1913 Webster]

   2. Overspread with something that resembles meal; as, the
      mealy wings of an insect. --Shak.
      [1913 Webster] mealybug

WordNet (r) 3.0 (2006):

mealy
    adj 1: containing meal or made of meal
    2: composed of or covered with particles resembling meal in
       texture or consistency; "granular sugar"; "the photographs
       were grainy and indistinct"; "it left a mealy residue" [syn:
       farinaceous, coarse-grained, grainy, granular,
       granulose, gritty, mealy]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "mealy":
   achromatic, achromic, anemic, ashen, ashy, bled white, bloodless,
   branny, cadaverous, chalklike, chalky, chloranemic, colorless,
   comminute, comminuted, crushed, dead, deadly pale, deathly pale,
   detrital, detrited, dim, dimmed, dingy, discolored, disintegrated,
   dull, dusty, efflorescent, etiolated, exsanguinated, exsanguine,
   exsanguineous, faded, faint, fallow, farinaceous, fine, flaky,
   flat, floury, furfuraceous, ghastly, gone to dust, grated, gray,
   ground, haggard, hueless, hypochromic, impalpable, lackluster,
   leaden, levigated, livid, lurid, lusterless, mat, milled, muddy,
   neutral, pale, pale as death, pale-faced, pallid, pasty, pestled,
   powdered, powdery, pulverant, pulverized, pulverulent,
   reduced to powder, sallow, scaly, scobicular, scobiform, scurfy,
   sharded, shredded, sickly, tallow-faced, toneless, triturated,
   uncolored, wan, washed-out, waxen, weak, whey-faced, white