Brawny, sinewy (8)
I believe the answer is:
muscular
This clue is a double definition.
'brawny' is the first definition.
(I know that brawny can be written as muscular)
'sinewy' is the second definition.
(I know that sinewy can be written as muscular)
(Other definitions for muscular that I've seen before include "Brawny, hefty" , "Powerful, strong" , "Robust (sort of Christianity)" , "Brawny, powerful in build" , "Beefy" .)