/ ˈɑːdjuəs; -dʒu-; NAmE ˈɑːrdʒuəs/ adjective
involving a lot of effort and energy, especially over a period of time :
an arduous journey across the Andes
The work was arduous.
► ar·du·ous·ly adverb
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WORD ORIGIN
mid 16th cent.: from Latin arduus steep, difficult + -ous .