The Collaborative International Dictionary of English v.0.48:

Belabor \Be*la"bor\, v. t. [imp. & p. p. Belabored; p. pr. &
   vb. n. Belaboring.]
   1. To ply diligently; to work carefully upon. "If the earth
      is belabored with culture, it yieldeth corn." --Barrow.
      [1913 Webster]

   2. To beat soundly; to cudgel.
      [1913 Webster]

            Ajax belabors there a harmless ox.    --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

belabor
    v 1: to work at or to absurd length; "belabor the obvious" [syn:
         belabor, belabour]
    2: attack verbally with harsh criticism; "She was belabored by
       her fellow students" [syn: belabor, belabour]
    3: beat soundly [syn: belabour, belabor]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "belabor":
   accent, accentuate, always trot out, baste, bastinado, batter,
   beat, belt, birch, buffet, cane, club, cowhide, cudgel, cut, drub,
   dwell on, dwell upon, emphasize, flagellate, flail, flog,
   fustigate, give a whipping, give emphasis to, give the stick,
   hammer away at, harp on, highlight, horsewhip, insist upon,
   italicize, knout, labor, lace, lambaste, lash, lay on,
   overaccentuate, overemphasize, overstress, pelt, pistol-whip,
   place emphasis on, point up, pommel, pound, pummel, punctuate,
   rawhide, rub in, scourge, smite, spank, spotlight, star, strap,
   stress, stripe, swinge, switch, thrash, thresh over, thump,
   trounce, truncheon, underline, underscore, wallop, whale, whip,
   whop