King that is first in Vietnamese capital (4)
I believe the answer is:
kiev
'capital' is the definition.
(capital of Ukraine)
'king that is first in vietnamese' is the wordplay.
'king' becomes 'K' (abbreviation for king in chess).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'first in vietnamese' becomes 'v' (1st letter of 'vietnamese').
'k'+'ie'+'v'='KIEV'
(Other definitions for kiev that I've seen before include "Capital city of the Ukraine" , "Ukraine's largest city" , "Ukrainian city" , "FC Dynamo/chicken ___" , "Ukrainian capital" .)