arduous

adj. difficult, hard, laborious, exhausting

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"
(synonym) backbreaking, grueling, gruelling, hard, heavy, laborious, punishing, toilsome
(similar) effortful
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
(synonym) straining, strenuous
(similar) effortful
3. difficult to accomplish; demanding considerable mental effort and skill; "the arduous work of preparing a dictionary"
(similar) difficult, hard

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

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

adj.
کٹھن , کشٹ , سخت , دشوار , بکٹ ,محنت کا , دوبھر
arduous task
کٹھن کام , کار دشوار

Synonyms and related words:
Herculean, abrupt, abstruse, backbreaking, brutal, burdensome, complex, critical, crushing, delicate, demanding, difficile, difficult, effortful, energetic, exacting, exhausting, fatiguing, forced, formidable, grueling, hairy, hard, heavy, hefty, intricate, jawbreaking, killing, knotted, knotty, labored, laborious, mean, no picnic, not easy, onerous, operose, oppressive, painful, precipitate, precipitous, punishing, rigorous, rough, rugged, set with thorns, severe, sheer, sideling, spiny, steep, stickle, strained, strenuous, taxing, thorny, ticklish, tiring, toilsome, tough, tricksy, tricky, troublesome, trying, uphill, vigorous, wearisome, wicked