The Collaborative International Dictionary of English v.0.48:

Labored \La"bored\, a.
   1. Bearing marks of labor and effort; elaborately wrought;
      not easy or natural; as, labored poetry; a labored style.
      [1913 Webster]

   2. appearing to require strong effort; as, labored breathing.

   Syn: heavy, laboured.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Labor \La"bor\, v. i. [imp. & p. p. Labored; p. pr. & vb. n.
   Laboring.] [OE. labouren, F. labourer, L. laborare. See
   Labor, n.] [Written also labour.]
   1. To exert muscular strength; to exert one's strength with
      painful effort, particularly in servile occupations; to
      work; to toil.
      [1913 Webster]

            Adam, well may we labor still to dress
            This garden.                          --Milton.
      [1913 Webster]

   2. To exert one's powers of mind in the prosecution of any
      design; to strive; to take pains.
      [1913 Webster]

   3. To be oppressed with difficulties or disease; to do one's
      work under conditions which make it especially hard,
      wearisome; to move slowly, as against opposition, or under
      a burden; to be burdened; -- often with under, and
      formerly with of.
      [1913 Webster]

            The stone that labors up the hill.    --Granville.
      [1913 Webster]

            The line too labors, and the words move slow.
                                                  --Pope.
      [1913 Webster]

            To cure the disorder under which he labored. --Sir
                                                  W. Scott.
      [1913 Webster]

            Come unto me, all ye that labor and are heavy laden,
            and I will give you rest.             --Matt. xi. 28
      [1913 Webster]

   4. To be in travail; to suffer the pangs of childbirth; to be
      in labor.
      [1913 Webster]

   5. (Naut.) To pitch or roll heavily, as a ship in a turbulent
      sea. --Totten.
      [1913 Webster]

WordNet (r) 3.0 (2006):

labored
    adj 1: lacking natural ease; "a labored style of debating" [syn:
           labored, laboured, strained]
    2: requiring or showing effort; "heavy breathing"; "the subject
       made for labored reading" [syn: heavy, labored,
       laboured]

Moby Thesaurus II by Grady Ward, 1.0:

104 Moby Thesaurus words for "labored":
   Herculean, Latinate, affected, alliterating, alliterative,
   arabesque, arduous, artificial, assonant, awkward, backbreaking,
   baroque, belabored, bombastic, burdensome, busy, chanting, chichi,
   chiming, cliche-ridden, clumsy, contrived, cramped, crushing,
   cumbrous, difficult, dingdong, effortful, elaborate, elegant,
   elephantine, excessive, fancy, farfetched, fine, flamboyant,
   florid, flowery, forced, formal, frilly, fussy, grueling, guinde,
   halting, hard, hard-earned, hard-fought, harping, heavy, hefty,
   high-wrought, humdrum, inept, inkhorn, jingle-jangle, jog-trot,
   killing, laborious, leaden, lumbering, luxuriant, luxurious,
   maladroit, monotone, monotonous, moresque, onerous, operose,
   oppressive, ornate, ostentatious, overdone, overelaborate,
   overelegant, overlabored, overworked, overwrought, painful,
   picturesque, pompous, ponderous, pretty-pretty, punishing, rhymed,
   rhyming, rich, rococo, sesquipedalian, singsong, stiff, stilted,
   strained, strenuous, tedious, toilsome, tough, troublesome, turgid,
   unnatural, unwieldy, uphill, wearisome, weighty