The Collaborative International Dictionary of English v.0.48:

Tiresome \Tire"some\, a.
   Fitted or tending to tire; exhausted; wearisome; fatiguing;
   tedious; as, a tiresome journey; a tiresome discourse. --
   Tire"some*ly, adv. -- Tire"some*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tiresomeness
    n 1: dullness owing to length or slowness [syn: tediousness,
         tedium, tiresomeness]