Quite good number by singer (10)
I believe the answer is:
altogether
'quite' is the definition.
(I've seen this before)
'good number by singer' is the wordplay.
'good' becomes 'g' (abbreviation).
'number' becomes 'ether' (anaesthetic, something which numbs).
'by' says to put letters next to each other.
'singer' becomes 'alto' (type of singing voice).
'g'+'ether'='gether'
'gether' put after 'alto' is 'ALTOGETHER'.
(Other definitions for altogether that I've seen before include "Completely, in total" , "Wholly" , "special to get Hermes trousers" , "Quite" , "totally" .)