Number ten raised by nine (5)
I believe the answer is:
nonet
'nine' is the definition.
(group of nine musicians)
'number ten raised' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'raised' shows that the letters should be reversed in order (going up in a down clue).
'ten' backwards is 'net'.
'no'+'net'='NONET'
'by' acts as a link.
(Other definitions for nonet that I've seen before include "Musical work for a set number of performers" , "Piece of music for nine" , "Piece for nine players" , "Piece for nine payers" , "Music for nine instruments or voices" .)