Primarily found in Japan, initially in Pacific (4)
I believe the answer is:
fiji
'pacific' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'primarily found in japan initially' is the wordplay.
'primarily' indicates taking the first letters.
The first letters of 'found in japan initially' is 'FIJI'.
'in' is the link.
Can you help me to learn more?
(Other definitions for fiji that I've seen before include "Pacific island member of the Commonwealth, capital Suva" , "Pacific island nation, capital Suva" , "Commonwealth state" , "South Pacific republic, capital Suva" , "Island group in the south Pacific" .)