Greek character has briefly purloined weapon (6)
I believe the answer is:
pistol
'weapon' is the definition.
(pistol is a kind of weapon)
'greek character has briefly purloined' is the wordplay.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'has' says to put letters next to each other.
'briefly' means to remove the last letter.
'purloined' becomes 'stole' (I've seen this before).
'stole' with its final letter taken off is 'stol'.
'pi'+'stol'='PISTOL'
(Other definitions for pistol that I've seen before include "Small firearm" , "Arm" , "making an appearance in Shakespeare's King Henry V" , "potential killer?" , "Small gun" .)