[ar.du.ous] adj [L arduus high, steep, difficult; akin to OIr ard high] (1538) 1 a: hard to accomplish or achieve: difficult "years of ~ training" b: marked by great labor or effort: strenuous "a life of ~ toil --A. C. Cole"
2: hard to climb: steep syn see hard -- ar.du.ous.ly adv -- ar.du.ous.ness n