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American Heritage Dictionary - Cite This Source - Share This

ar·du·ous       (är'jōō-əs)  Pronunciation Key  adj.   Demanding great effort or labor; difficult: "the arduous work of preparing a Dictionary of the English Language" (Thomas Macaulay). Testing severely the powers of endurance; strenuous: a long, arduous, and exhausting war. Hard to traverse, climb, or surmount. See Synonyms at burdensome, hard. [From Latin arduus, high, steep.] ar'du·ous·ly adv., ar'du·ous·ness n.

Online Etymology Dictionary - Cite This Source - Share This
arduous 

WordNet - Cite This Source - Share This

arduous
adjective
1.	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"
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.Roosevelt
3.	difficult to accomplish; demanding considerable mental effort and skill; "the arduous work of preparing a dictionary"

Webster's Revised Unabridged Dictionary - Cite This Source - Share This

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."