We peek inside to see the weapon (4)
I believe the answer is:
epee
'the weapon' is the definition.
(epee is a kind of weapon)
'we peek inside' is the wordplay.
'inside' says the answer is hidden in the clue.
'EPEE' is hidden within 'we peek'.
'to see' acts as a link.
(Other definitions for epee that I've seen before include "Fencing weapon" , "Duelling weapon" , "Fencing sword, heavier than a foil" , "Rapier" , "Fencer's weapon" .)