Reverberation in the choir (4)
I believe the answer is:
echo
'reverberation' is the definition.
('echo' can be a synonym of 'reverberation')
'in the choir' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ECHO' can be found hidden inside 'the choir'.
(Other definitions for echo that I've seen before include "Mimic" , "Reflected radar beam" , "Trace call" , "Nymph (only able to repeat the last words of others)" , "Repeating of sound" .)