Country that has to help Northern Ireland in return (5)
I believe the answer is:
india
'country' is the definition.
(I know that India is a country)
'to help northern ireland in return' is the wordplay.
'to help' becomes 'aid' (synonyms).
'northern ireland' becomes 'NI' (abbreviation).
'in return' shows that the letters should be reversed in order (return can mean to go backwards).
'aid'+'ni'='aidni'
'aidni' back-to-front is 'INDIA'.
'that has' is the link.
(Other definitions for india that I've seen before include "Country; I (radio alphabet)" , "Type of paper, rubber etc" , "IDA in the country?" , "Bollywood's country" , "Code for the letter I" .)