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