The most common and most likely answer to this crossword clue is the 8 letter word STARTLES
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More clues leading to the result STARTLES
Buddy explains!

The straight part
We know that "Unsettles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unsettles = startles.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 STARTLES mean?
STARTLES noun- A sudden motion or shock caused by an unexpected alarm, surprise, or apprehension of danger.
- To move suddenly, or be excited, on feeling alarm; to start.
- To excite by sudden alarm, surprise, or apprehension; to frighten suddenly and not seriously; to alarm; to surprise.
- To deter; to cause to deviate.