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):

laboriousness
    n 1: the quality of requiring extended effort [syn:
         laboriousness, operoseness, toilsomeness]