The most common and most likely answer to this crossword clue is the 5 letter word INCAS
I've seen this crossword clue in The Times
I
N
C
A
S
More clues leading to the result INCAS
- Americans once using dollar bills, leaving hospital
- As a precaution, not taking all native people
- Peruvians once home get lots of money
- People now lost, if briefly
- Old people’s home about to shut – basic accommodation lacking
- Ancient people imprisoned in Dublin Castle
- Ancient people, practitioners of tattoo art some said?
- Indian people invading mountain castle
- Discovered mint with money mainly for South Americans
- People annexed by Spain
Buddy explains!

The straight part
We know that "Peruvians once" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case peruvians once = incas.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INCAS mean?
INCAS noun- Any of several species of hummingbirds in the genus Coeligena