Sword carried by the peer (4)
I believe the answer is:
epee
'sword' is the definition.
(sword used in fencing)
'carried by the peer' is the wordplay.
'carried by' indicates a hidden word.
'EPEE' can be found hidden inside 'the peer'.
(Other definitions for epee that I've seen before include "Type of sword" , "Sharp-pointed duelling sword" , "Fencing sword similar to a foil" , "sports equipment" , "Olympic event" .)