Legendary musketeer in combat, hostile (5)
I believe the answer is:
athos
'legendary musketeer' is the definition.
(character in The Three Musketeers)
'in combat hostile' is the wordplay.
'in' says the answer is hidden in the clue.
'ATHOS' is hidden within 'combat hostile'.
(Other definitions for athos that I've seen before include "Appropriating" , "Dumas musketeer" , "Greek mountain; one of the three musketeers" , "Colleague of Porthos, Aramis" , "Literary musketeer" .)