1. (adj.)arduous requiring great exertion; laborious: arduous tasks.
2. arduous usingmuch energy; strenuous: an arduous effort.
3. arduous hard to climb; steep: an arduous path.
4. arduous full of hardships; severe: an arduous winter.
Etymology: (bef. 900; ME aren, are, arn, OE aron; c. ON eru. See art2)
Definition of 'arduous'
Princeton's WordNet
1. (adj)arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome 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. (adj)arduous, straining, strenuous 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. (adj)arduous difficult to accomplish; demanding considerable mental effort and skill "the arduous work of preparing a dictionary"
Definitions of arduous 
Afrikaans: swaar, moeisaam
Arabic: شاق، مُرهِق
Bulgarian: тежък
Brazilian: árduo
Czech: obtížný, pracný, svízelný
German: mühselig
Danish: vanskelig; besværlig
Greek: επίπονος, κοπιώδης
Spanish: arduo
Estonian: vaevaline
Farsi: دشوار؛ طاقت فرسا
Finnish: työläs
French: ardu
Hebrew: כָּרוּך בְּמַאֲמָצִים
Hindi: श्रमसाध्य
Croatian: gorljiv
Hungarian: nehéz
Indonesian: sulit, sukar
Icelandic: erfiður
Italian: arduo
Japanese: 骨の折れる
Korean: 힘든
Lithuanian: sunkus, varginantis
Latvian: grūts; spraigs
Malay: sukar
Dutch: lastig, zwaar
Norwegian: vanskelig, anstrengende
Polish: żmudny
Persian: دشوار؛ طاقت فرسا
Pashto: ستونزمن
Portuguese: penoso
Romanian: dificil
Russian: трудный
Slovak: náročný
Slovenian: težaven
Serbian: naporan
Swedish: svår, mödosam
Thai: ยากลำบาก
Turkish: zor, güç
Taiwanese: 艱巨的
Ukrainian: важкий, напружений
Urdu: پُر مشقت
Vietnamese: khó khăn
Chinese: 艰巨的
