The most common and most likely answer to this crossword clue is the 8 letter word SOOTHING
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Buddy explains!

The straight part
We know that "Composing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case composing = soothing.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 SOOTHING mean?
SOOTHING verb- To restore to ease, comfort, or tranquility; relieve; calm; quiet; refresh.
- To allay; assuage; mitigate; soften.
- To smooth over; render less obnoxious.
- To calm or placate someone or some situation.
- To ease or relieve pain or suffering.
- To temporise by assent, concession, flattery, or cajolery.
- To bring comfort or relief.
- To keep in good humour; wheedle; cajole; flatter.
- To prove true; verify; confirm as true.
- To confirm the statements of; maintain the truthfulness of (a person); bear out.
- To assent to; yield to; humour by agreement or concession.
- The act by which somebody is soothed.
- Tending to soothe.
- Giving relief.
- Freeing from fear or anxiety.