Of an ancient Andean culture (5)
I believe the answer is:
incan
'of an ancient andean culture' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for incan that I've seen before include "Imperialist of the past" , "From old Peru" , "like former S American civilisation" , "Old Peruvian" , "Of an ancient Andean culture" .)