An organ at each end of the choir (3)
I believe the answer is:
ear
'an organ' is the definition.
(the ear is an organ)
'at each end of the choir' is the wordplay.
'at' means one lot of letters go next to another.
'each' becomes 'ea' (abbreviation).
'end of the' indicates one should take the final letters.
The last letter of 'choir' is 'r'.
'ea'+'r' is 'EAR'.
(Other definitions for ear that I've seen before include "Musical appreciation" , "Seed-bearing part of wheat" , "That makes sense" , "willingness to listen" , "Discernment musicians need" .)