Voice back in order, one thinks (5)
I believe the answer is:
tenor
'voice' is the definition.
(one of the voices in a choir say)
'back in order one thinks' is the wordplay.
'back' is a reversal indicator.
'in' indicates the answer is hidden within the clue.
'ronet' is hidden within 'order one thinks'.
'ronet' back-to-front is 'TENOR'.
(Other definitions for tenor that I've seen before include "Male singer with high register" , "Eg, Luciano Pavarotti" , "High male singing voice like Pavarotti" , "range of 14 across [GIGLI]" , "direction" .)