Thai leader held by Japanese leader yields weapon (7)
I believe the answer is:
shotgun
'weapon' is the definition.
(shotgun is a kind of weapon)
'thai leader held by japanese' is the wordplay.
'thai leader' becomes 't' (I can't justify this - if you can you should give a lot more credence to this answer).
'held by' indicates putting letters inside.
'japanese' becomes 'shogun' (shogun is a kind of japanese).
't' put within 'shogun' is 'SHOTGUN'.
'leader yields' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for shotgun that I've seen before include "No thugs (anag) - weapon" , "piece" , "arm" , "Firearm used at short range - kind of wedding" , "Hunting firearm" .)