arduous

adjective

1. 1

   difficult to accomplish; demanding considerable mental effort and skill

   the arduous work of preparing a dictionary

2. 2

   characterized by effort to the point of exhaustion; especially physical effort

   worked their arduous way up the mining valley

   a grueling campaign

3. 3

   taxing to the utmost; testing powers of endurance

   his final, straining burst of speed

   a strenuous task