arduousyoudaoicibaDictYouDict[arduous 词源字典]
arduous: [16] Latin arduus, the source of English arduous, originally meant ‘high, steep’ (it is related to Greek orthós ‘straight, upright, correct’, as in English orthodox); the sense ‘difficult, laborious’ was a later metaphorical development. (The word has no connection with ardour, which comes ultimately from Latin ardēre ‘burn’; see ARSON.)
=> orthodox[arduous etymology, arduous origin, 英语词源]
arduous (adj.)youdaoicibaDictYouDict
1530s, "hard to accomplish, difficult to do," from Latin arduus "high, steep," also figuratively, "difficult," from PIE root *eredh- "to grow, high" (see ortho-). Literal sense of "high, steep, difficult to climb," attested in English from 1709.