- arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, punishing, toilsome - 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"
Antonym: effortless (indirect, via effortful)