Adjective
1. characterized by toilsome 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"2. 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.Roosevelt3. difficult to accomplish; demanding considerable mental effort and skill;
"the arduous work of preparing a dictionary"