Greek character nicked sawn-off weapon (6)
I believe the answer is:
pistol
'weapon' is the definition.
(pistol is a kind of weapon)
'greek character nicked sawn-off' is the wordplay.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'nicked' becomes 'stole' (nick can mean to steal).
'sawn-off' means to remove the last letter.
'stole' with its final letter removed is 'stol'.
'pi'+'stol'='PISTOL'
(Other definitions for pistol that I've seen before include "Small gun" , "Rectangular" , "Shakespearean - weapon" , "A small hand-gun" , "Small firearm" .)