The most common and most likely answer to this crossword clue is the 4 letter word PACT
I've seen this crossword clue in The Times
P
A
C
T
More clues leading to the result PACT
- Quiet piece of legislation to secure treaty
- Having little wriggle room, as they say, for a settlement
- Auditor's full agreement
- Agreement in a case, we hear?
- Announced very full agreement
- Quiet deed brings agreement
- Agreement leads to peace and calmer times
- Peel's first deed, producing treaty
- The Speaker’s prepared case for agreement
- Convention full of people, I’m told
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 = pact.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 PACT mean?
PACT noun- An agreement; a compact; a covenant.
- An agreement between two or more nations
- To form a pact; to agree formally.