Source : Webster's Revised Unabridged Dictionary (1913)

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

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

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

Source : WordNet®

laborious
     adj : characterized by toilsome effort to the point of exhaustion;
           especially physical effort; "worked their arduous way
           up the mining valley"; "a grueling campaign"; "hard
           labor"; "heavy work"; "heavy going"; "spent many
           laborious hours on the project"; "set a punishing pace"
           [syn: {arduous}, {backbreaking}, {grueling}, {gruelling},
            {hard}, {heavy}, {punishing}, {toilsome}]