The Collaborative International Dictionary of English v.0.48:

Toilsome \Toil"some\ (toil"s[u^]m), a.
   Attended with toil, or fatigue and pain; laborious;
   wearisome; as, toilsome work.
   [1913 Webster]

         What can be toilsome in these pleasant walks? --Milton.
   [1913 Webster] -- Toil"some*ly, adv. -- Toil"some*ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

toilsome
    adj 1: characterized by 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,
           laborious, operose, punishing, toilsome]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "toilsome":
   Herculean, abstruse, arduous, backbreaking, brutal, burdensome,
   complex, critical, crushing, delicate, demanding, difficile,
   difficult, draining, effortful, enervating, exacting, exhausting,
   fatiguesome, fatiguing, forced, formidable, grueling, hairy, hard,
   hard-earned, hard-fought, heavy, hefty, intricate, jawbreaking,
   killing, knotted, knotty, labored, laborious, mean, no picnic,
   not easy, onerous, operose, oppressive, painful, punishing,
   rigorous, rough, rugged, set with thorns, severe, spiny, steep,
   strained, straining, strenuous, stressful, thorny, ticklish,
   tiresome, tiring, tough, tricky, troublesome, trying, uphill,
   weariful, wearing, wearisome, wearying, wicked