Thickset, stocky (5)
I believe the answer is:
burly
This clue is a double definition.
'thickset' is the first definition.
(I've seen this in another clue)
'stocky' is the second definition.
(I've seen this before)
(Other definitions for burly that I've seen before include "Muscular; strapping" , "Big and thickset" , "Muscular and heavily built" , "Big and sturdy" , "Sturdily built" .)