Starts to boycott another North Korean financial institution (4)
I believe the answer is:
bank
'financial institution' is the definition.
(bank is a kind of financial institution)
'starts to boycott another north korean' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'boycott another north korean' is 'BANK'.
(Other definitions for bank that I've seen before include "Financial institution - riverside" , "Edge (of river) - tier (of oars)" , "Reserve" , "Sloping land" , "area by river" .)