Cryptic crossword clue
Turn off – this can end disastrously 10

The most common and most likely answer to this crossword clue is the 10 letter word DISENCHANT

I've seen this crossword clue in Financial Times
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Buddy explains!

The straight part
We know that "Turn off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case turn off = disenchant.
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 DISENCHANT mean?

DISENCHANT verb
  1. (of a person) To free from illusion, false belief or enchantment; to undeceive or disillusion.
  2. (of a person) To disappoint.
  3. (of a thing) To remove a spell or magic enchantment from.

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