Very arduous, having feet (4)
I believe the answer is:
yard
'feet' is the definition.
(I have seen 'several feet' mean 'yard' so perhaps 'feet' could also mean 'yard')
'very arduous having' is the wordplay.
'having' indicates a hidden word.
'YARD' is hidden in the letters of 'very arduous'.
(Other definitions for yard that I've seen before include "Thirty six inches" , "Unit of distance" , "quantity of ale" , "short distance" , "Enclosure by house" .)