Empty room sound (4)
I believe the answer is:
echo
'empty room sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for echo that I've seen before include "Reflect sound" , "Be suggestive of" , "In The Maid of the Mountains" , "Send back" , "Reverberate - nymph spurned by Narcissus" .)