King leaving boat in East thanks military leaders (5)
I believe the answer is:
junta
'military leaders' is the definition.
(as in a military junta ruling by martial law)
'king leaving boat in east thanks' is the wordplay.
'king' becomes 'K' (abbreviation for king in chess).
'leaving' indicates named letters should be taken away.
'boat in east' becomes 'junk' (type of Asian ship).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'junk' with 'k' removed is 'jun'.
'jun'+'ta'='JUNTA'
(Other definitions for junta that I've seen before include "Military regime" , "Ruling military body after forced takeover" , "Unelected military government" , "Military group ruling after a coup" , "Military cabal" .)