Definitions of arduous:

• adjective:   difficult to accomplish; demanding considerable mental effort and skill

  Example: "The arduous work of preparing a dictionary"

• adjective:   characterized by toilsome effort to the point of exhaustion; especially physical effort

  Example: "Worked their arduous way up the mining valley"

• adjective:   taxing to the utmost; testing powers of endurance

  Example: "Your willingness after these six arduous days to remain here- F.D.Roosevelt"