Lean and sinewy (4)
I believe the answer is:
wiry
'lean and sinewy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wiry that I've seen before include "Lean, tough, sinewy" , "Strong and flexible" , "with coarse hair" , "strong and slim" , "Slender but strong and agile" .)