Sword combative peer sheathes (4)
I believe the answer is:
epee
'sword' is the definition.
(sword used in fencing)
'combative peer sheathes' is the wordplay.
'sheathes' indicates a hidden word (the answer is covered or sheathed by the clue).
'EPEE' can be found hidden inside 'combative peer'.
(Other definitions for epee that I've seen before include "Fencing sword, heavier than a foil" , "Thin fencing sword" , "Duelling weapon" , "Pointed weapon" , "Sharp-pointed duelling sword" .)