Source : WordNet®

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}]