Diplomats ignoring mad rebels holding weapon (6)
I believe the answer is:
pistol
'weapon' is the definition.
(pistol is a kind of weapon)
'diplomats ignoring mad rebels' is the wordplay.
'ignoring' indicates named letters should be taken away.
'rebels' is an anagram indicator.
'diplomats' with 'mad' removed is 'iplots'.
'iplots' with letters rearranged gives 'PISTOL'.
'holding' is the link.
(Other definitions for pistol that I've seen before include "making an appearance in Shakespeare's King Henry V" , "Hand weapon" , "Type of gun" , "Rectangular" , "Shakespearean character" .)