I help Northern Island from the south (5)
I believe the answer is:
india
'i' is the definition.
(India is I in the NATO phonetic alphabet)
'help northern island from the south' is the wordplay.
'help' becomes 'aid' (synonyms).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'island' becomes 'i'.
'from the south' says the letters should be written in reverse (in a down clue, letters go up).
'aid'+'n'+'i'='aidni'
'aidni' backwards is 'INDIA'.
(Other definitions for india that I've seen before include "In aid, strangely, of the country" , "Populous nation" , "The world's most populous democracy" , "One preceding Juliet" , "Place of Kipling's birth" .)