The most common and most likely answer to this crossword clue is the 5 letter word ALTOS
I've seen this crossword clue in The Daily Telegraph
A
L
T
O
S
More clues leading to the result ALTOS
- They appear in recital to sing
- Part of choir split up in rehearsal to sing
- Choir members in cathedral to sing
- A line taking tenor over soprano or other choir members
- Might they take part in musical, to sing?
- Key thus backfiring for singers
- Part of choir having article lost at sea
- Two notes returned ringing little tenor voices
- They are used to having high scores
- Singers regularly using ballet tops
Buddy explains!

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 ALTOS mean?
ALTOS noun- A musical part or section higher than tenor and lower than soprano, formerly the part that performed a countermelody above the tenor or main melody.
- A person or musical instrument that performs the alto part.
- An alto saxophone