The most common and most likely answer to this crossword clue is the 9 letter word WELL-BRED
I've seen this crossword clue in The Guardian
W
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More clues leading to the result WELL-BRED
Buddy explains!
The straight part
We know that "Polite" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case polite = well-bred.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 WELL-BRED mean?
WELL-BRED adjective- (of animals) Of good breed.
- (by extension) Well-mannered and refined because of a good upbringing and education.