The most common and most likely answer to this crossword clue is the 10 letter word STABILISER
I've seen this crossword clue in The Guardian
S
T
A
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More clues leading to the result STABILISER
Buddy explains!
The straight part
We know that "settler" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case settler = stabiliser.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 STABILISER mean?
STABILISER noun- Any person or thing that brings stability.
- Any substance added to something in order to stabilize it.
- A gyroscopically controlled fin or similar device that prevents the excess rolling of a ship in rough seas.
- An airfoil that stabilizes the flight of an aircraft or missile.
- A piece of backing fabric used in embroidery.