形容詞 arduous:

1. characterized by toilsome effort to the point of exhaustion; especially physical effort
   同義詞：backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome
2. taxing to the utmost; testing powers of endurance- F.D.Roosevelt
   同義詞：straining, strenuous
3. difficult to accomplish; demanding considerable mental effort and skill

1. Negotiating a reduction in nuclear arms is a long and arduous undertaking.
   有關(guān)削減核武器的談判是一項漫長而艱苦的工作
2. He mastered these words through the arduous consultation of the dictionary.
   通過勤查字典，他掌握了這些單詞。
3. Although the work was arduous, he finished it in a short time.
   雖然這項工作很費力，他仍然很快就做完了。
4. It's an arduous task.
   這是一項艱巨的任務(wù)。

ar.du.ous

adj.（形容詞）
Demanding great effort or labor; difficult:
艱巨的：需要很大努力或工作的；困難的：
例句：
.the arduous work of preparing a Dictionary of the English Language.(Macaulay)
.制作一本英語語言詞典的艱巨工作.(麥考利)

Testing severely the powers of endurance; strenuous:
艱難的：忍耐力的嚴(yán)格考驗的；艱苦的：
例句：
a long, arduous, and exhausting war.
一次長期、艱難而疲憊不堪的戰(zhàn)爭

Hard to traverse, climb, or surmount.See Synonyms at burdensome ,hard
難攀登的，陡峭的：難以通過、攀登或克服的參見 burdensome,hard

來源：
From Latin arduus [high, steep]
源自 拉丁語 arduus [高的，陡峭的]

【引伸】
ar.duously
adv.（副詞）
ar.duousness
n.（名詞）