Rolling Stones out for musical instruction (9)

I believe the answer is:

sostenuto

I'm a little stuck... Click here to teach me more about this clue!

'for musical instruction' is the definition.
I can't tell whether this defines the answer.

'rolling stones out' is the wordplay.
'rolling' indicates an anagram.
'stones'+'out'='stonesout'
'stonesout' anagrammed gives 'SOSTENUTO'.

Can you help me to learn more?

(Other definitions for sostenuto that I've seen before include "musical movement" , "In this way" , "smoothly, not letting up" .)

I've seen this clue in the Sydney Morning Herald.

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