arduous

Adjective

• difficult to accomplish; demanding considerable mental effort and skill
  • the arduous work of preparing a dictionary
    

• 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
    

• 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
    

Related words

• Synonyms: 
  straining , strenuous