From WordNet (r) 2.0 (August 2003) [wn]:
backbreaking
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, grueling, gruelling, hard,
heavy, laborious, punishing, toilsome]