Singer in choir, one tarted up (5)
I believe the answer is:
tenor
'singer' is the definition.
(I know that tenor is a type of singer)
'in choir one tarted up' is the wordplay.
'in' indicates the answer is hidden within the clue.
'up' is a reversal indicator (in down clue: letters go upwards).
'ronet' can be found hidden inside 'choir one tarted'.
'ronet' back-to-front is 'TENOR'.
(Other definitions for tenor that I've seen before include "One singing" , "Male singer with high register" , "Eg, Luciano Pavarotti" , "exact words" , "High male singing voice like Pavarotti" .)