Amazonian people in one place to the north (4)
I believe the answer is:
tupi
'amazonian people in' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'one place to the north' is the wordplay.
'one' becomes 'i' (roman numeral).
'place' becomes 'put' (synonyms).
'to the north' says the letters should be written backwards (in a down clue, letters go up or 'northward').
'i'+'put'='iput'
'iput' backwards is 'TUPI'.
Can you help me to learn more?
(Other definitions for tupi that I've seen before include "Amazon language" , "Amazonian language" .)