The most common and most likely answer to this crossword clue is the 11 letter word ARBITRATION
I've seen this crossword clue in The Guardian
A
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Buddy explains!
The straight part
We know that "settlement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case settlement = arbitration.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 ARBITRATION mean?
ARBITRATION noun- The act or process of arbitrating.
- A process through which two or more parties use an arbitrator or arbiter in order to resolve a dispute.
- In general, a form of justice where both parties designate a person whose ruling they will accept formally. More specifically in Market Anarchist (market anarchy) theory, arbitration designates the process by which two agencies pre-negotiate a set of common rules in anticipation of cases where a customer from each agency is involved in a dispute.