The most common and most likely answer to this crossword clue is the 13 letter word CONDESCENDING
I've seen this crossword clue in The Guardian
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More clues leading to the result CONDESCENDING
- Seeing fit Conservative on the way down
- Supercilious prisoner’s going down
- Snooty prisoner sent down?
- Supercilious cheat going down
- Disdainful prisoner being sent down
- Caught on — going down or stuck-up?
- Criminal coming down, patronizing
- First customer's agreed for coming down and patronising
- Supercilious crook dropping down
Buddy explains!

The straight part
We know that "Supercilious" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supercilious = condescending.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 CONDESCENDING mean?
CONDESCENDING verb- To come down from one's superior position; to deign (to do something).
- To treat (someone) as though inferior; to be patronizing (toward someone); to talk down (to someone).
- (possibly nonstandard) To treat (someone) as though inferior; to be patronizing toward (someone); to talk down to (someone).
- To consent, agree.
- To come down.
- Assuming a tone of superiority, or a patronizing attitude.