The most common and most likely answer to this crossword clue is the 6 letter word TENUTO
I've seen this crossword clue in Independent
T
E
N
U
T
O
More clues leading to the result TENUTO
- Sustained note in number just now oddly falling away
- Sustained section of allegretto tune totally recalled
- Note – ut, possibly – kept going for longer
- Sustained tune to broadcast
- Sustained melody with time roused love
- Figure out confusing musical expression
- d Sustained work done by fielding side, having dropped opposition’s opener
Buddy explains!

The straight part
We know that "Sustained note" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sustained note = tenuto.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 TENUTO mean?
TENUTO noun- A tempo mark directing that a note or passage is to be held for the full time
- A passage having this mark
- Describing a passage having this mark
- In a sustained manner