Silly commander, one showing weapon (7)
I believe the answer is:
assagai
'weapon' is the definition.
(assagai is a kind of weapon)
'silly commander one' is the wordplay.
'silly' becomes 'ass'.
'commander' becomes 'aga' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'ass'+'aga'+'i'='ASSAGAI'
'showing' acts as a link.
(Other definitions for assagai that I've seen before include "Zulu weaponry" , "Weapon" , "Spear used in S Africa" .)