The Collaborative International Dictionary of English v.0.48:

Lackluster \Lack"lus`ter\, Lacklustre \Lack"lus`tre\, n.
   A lack of luster.
   [1913 Webster] Lackluster

The Collaborative International Dictionary of English v.0.48:

Lackluster \Lack"lus`ter\, Lacklustre \Lack"lus`tre\ a.
   1. Wanting luster or brightness. "Lackluster eye." --Shak.
      [1913 Webster]

   2. Lacking spirit, liveliness, or enthusiasm; dull.
      [PJC]

   3. Mediocre; as, a lackluster performance.
      [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "lackluster":
   absence of color, achromatic, achromaticity, achromatism, achromic,
   anemic, ashen, ashy, betwixt and between, bled white, blind,
   bloodless, cadaverous, chloranemic, colorless, colorlessness, dead,
   deadened, deadly pale, deathly pale, dim, dimmed, dingy,
   discolored, drab, dull, dullness, etiolated, exsanguinated,
   exsanguine, exsanguineous, faded, faint, fair, fair to middling,
   fairish, fairishness, fallow, flat, ghastly, gray, haggard,
   hueless, huelessness, hypochromic, indifference, indifferent,
   insipid, leaden, lifeless, livid, lurid, lusterless, mat, mealy,
   mediocre, mediocreness, mediocrity, medium, middling, middlingness,
   moderate, moderateness, modest, modestness, modesty, muddy, muted,
   namby-pamby, neutral, of a kind, of a sort, of sorts, pale,
   pale as death, pale-faced, pallid, passable, passableness, pasty,
   prosaic, prosy, respectability, respectable, rusty, sallow, sickly,
   so-so, somber, tallow-faced, tarnished, tedious, tediousness,
   tolerable, tolerableness, toneless, tonelessness, uncolored, vapid,
   wan, washed-out, waxen, weak, whey-faced, white, wishy-washy