The weapons are a knock out, sire! (7)
I believe the answer is:
rapiers
'the weapons' is the definition.
(rapier is a kind of weapon)
'a knock out sire' is the wordplay.
'a knock' becomes 'rap' (synonyms).
'out' indicates anagramming the letters.
'sire' with letters rearranged gives 'iers'.
'rap'+'iers'='RAPIERS'
'are' acts as a link.
(Other definitions for rapiers that I've seen before include "Double-edged swords" , "Straight swords with narrow blades" .)