A doctor in South Africa or in the Pacific (5)
I believe the answer is:
samoa
'in the pacific' is the definition.
(I know that Samoa is part of Polynesia)
'a doctor in south africa' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'in' means one lot of letters goes inside another.
'south africa' becomes 'SA' (abbreviation).
'a'+'mo'='amo'
'amo' going within 'sa' is 'SAMOA'.
'or' is the link.
(Other definitions for samoa that I've seen before include "island territory" , "South-west Pacific nation" , "Group of islands in the South Pacific" , "South Pacific island nation" , "Southwest Pacific island group" .)