The most common and most likely answer to this crossword clue is the 9 letter word CREEPIEST
I've seen this crossword clue in The Guardian
C
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More clues leading to the result CREEPIEST
Buddy explains!
The straight part
We know that "most disturbing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most disturbing = creepiest.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 CREEPIEST mean?
CREEPIEST adjective- Moving by creeping along.
- Producing an uneasy fearful sensation, as of things crawling over one's skin.
- Feeling an uneasy fearful sensation; creeped out.
- Strangely repulsive.