I drift north from Polynesia, originally (5)
I believe the answer is:
maori
'from polynesia originally' is the definition.
(the Maori are aboriginal Polynesian people)
'i drift north' is the wordplay.
'drift' becomes 'roam' (synonyms).
'north' is a reversal indicator (in a down clue, letters go up or 'northward').
'i'+'roam'='iroam'
'iroam' in reverse letter order is 'MAORI'.
(Other definitions for maori that I've seen before include "Native language of NZ" , "race" , "Member of New Zealand's aboriginal people" , "Native New Zealanders" , "Aboriginal New Zealander" .)