Strenuous (7)
'strenuous' is the definition.
(synonyms)
This is all the clue.
(Other definitions for arduous that I've seen before include "Steep; laborious" , "Demanding great effort" , "Gruelling, strenuous" , "Requiring much effort" , "Requiring great effort" .)
'strenuous' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for taxing that I've seen before include "Getting money off people" , "Physically or mentally demanding" , "Making great demands" , "Making heavy demands, like Revenue Commissioners" , "hard work" .)