Reverberation in City house (4)
I believe the answer is:
echo
'reverberation' is the definition.
('echo' can be a synonym of 'reverberation')
'city house' is the wordplay.
'city' becomes 'ec' (the City of London postcode).
'house' becomes 'ho' (abbreviation for house).
'ec'+'ho'='ECHO'
'in' is the link.
(Other definitions for echo that I've seen before include "Response" , "Reflect sound" , "Comms code word for E" , "One who slavishly copies" , "Radio operator's word for 'E'" .)