arduous in WordNet English dictionary

1. difficult to accomplish; demanding considerable mental effort and skill
   "the arduous work of preparing a dictionary"
   arduous 
   
2. 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  backbreaking  grueling  gruelling  hard  heavy  laborious  operose  punishing  toilsome 
   
3. 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  straining  strenuous