Cryptic crossword clue
Drained after tight run-out, remaining calm 10

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

I've seen this crossword clue in The Guardian
U
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Buddy explains!

The straight part
We know that "remaining calm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case remaining calm = untroubled.
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 UNTROUBLED mean?

UNTROUBLED adjective
  1. Without worries; free from care.

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