The Collaborative International Dictionary of English v.0.48:

Torturous \Tor"tur*ous\ (t[^o]r"t[-u]r*[u^]s), a.
   Involving, or pertaining to, torture. [R.] "The torturous
   crucifixion." --I. Disraeli.
   [1913 Webster]

WordNet (r) 3.0 (2006):

torturous
    adj 1: extremely painful [syn: agonizing, agonising,
           excruciating, harrowing, torturing, torturous,
           torturesome]