Muscular, but not exactly a bully (5)
I believe the answer is:
burly
'muscular' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for burly that I've seen before include "Big and sturdy" , "Strongly and heavily built" , "Sturdily built" , "Muscular; strapping" , "Big and thickset" .)