The most common and most likely answer to this crossword clue is the 5 letter word CAJUN
I've seen this crossword clue in The Sunday Telegraph
C
A
J
U
N
Buddy explains!

The straight part
We know that "descended from French colonists" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case descended from french colonists = cajun.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 CAJUN mean?
CAJUN adjective- Relating to the Cajun people or their culture.
- Of spicy food prepared in the style of the Cajun cuisine.