Arduous \Ar"du*ous\ (?; 135), a. [L. arduus steep, high; akin to Ir. ard high, height.]

1. Steep and lofty, in a literal sense; hard to climb.

Those arduous paths they trod. --Pope.

2. Attended with great labor, like the ascending of acclivities; difficult; laborious; as, an arduous employment, task, or enterprise.

Syn: Difficult; trying; laborious; painful; exhausting.

Usage: Arduous, Hard, Difficult. Hard is simpler, blunter, and more general in sense than difficult; as, a hard duty to perform, hard work, a hard task, one which requires much bodily effort and perseverance to do. Difficult commonly implies more skill and sagacity than hard, as when there is disproportion between the means and the end. A work may be hard but not difficult. We call a thing arduous when it requires strenuous and persevering exertion, like that of one who is climbing a precipice; as, an arduous task, an arduous duty. ``It is often difficult to control our feelings; it is still harder to subdue our will; but it is an arduous undertaking to control the unruly and contending will of others.''

Source: Webster's Revised Unabridged Dictionary (1913)