ar ‧ du ‧ ous /ˈɑːdjuəs $ ˈɑːrdʒuəs/ BrE AmE adjective
[ Date: 1500-1600 ; Language: Latin ; Origin: arduus 'high, steep, difficult' ]
involving a lot of strength and effort
arduous task/work
the arduous task of loading all the boxes into the van
arduous journey/voyage
an arduous journey through the mountains
—arduously adverb