The Collaborative International Dictionary of English v.0.48:

Laborious \La*bo"ri*ous\, a. [L. laboriosus, fr. labor labor:
   cf. F. laborieux.]
   1. Requiring labor, perseverance, or sacrifices; toilsome;
      tiresome.
      [1913 Webster]

            Dost thou love watchings, abstinence, or toil,
            Laborious virtues all? Learn these from Cato.
                                                  --Addison.
      [1913 Webster]

   2. Devoted to labor; diligent; industrious; as, a laborious
      mechanic.
      [1913 Webster] -- La*bo"ri*ous*ly, adv. --
      La*bo"ri*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

laboriously
    adv 1: in a laborious manner; "their lives were spent in
           committee making decisions for others to execute on the
           basis of data laboriously gathered for them"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "laboriously":
   ardently, arduously, assiduously, bec et ongles, burdensomely,
   difficultly, diligently, effortfully, energetically, fervently,
   hammer and tongs, hard, hardly, heart and soul, indefatigably,
   industriously, manfully, onerously, operosely, painfully,
   relentlessly, sedulously, strenuously, the hard way, tirelessly,
   toilsomely, tooth and nail, unsparingly, vehemently, with a will,
   with difficulty, with effort, with much ado, zealously