arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome (adj)

characterized by 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"

arduous, straining, strenuous (adj)

taxing to the utmost; testing powers of endurance

"his final, straining burst of speed"; "a strenuous task"; "your willingness after these six arduous days to remain here"- F.D.Roosevelt

arduous (adj)

difficult to accomplish; demanding considerable mental effort and skill

"the arduous work of preparing a dictionary"

arduous (Adjective)

Needing or using up much energy; testing powers of endurance.

arduous (Adjective)

burning; ardent

arduous (Adjective)

Difficult or exhausting to traverse.