The most common and most likely answer to this crossword clue is the 9 letter word STILLNESS
I've seen this crossword clue in Independent
S
T
I
L
L
N
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S
More clues leading to the result STILLNESS
Buddy explains!
The straight part
We know that "Calm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calm = stillness.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 STILLNESS mean?
STILLNESS noun- The quality or state of being still
- Habitual silence or quiet; taciturnity.