Repeating sound (4)
I believe the answer is:
echo
'repeating sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for echo that I've seen before include "Nymph; E (radio comms.)" , "Repeated sound" , "repeated answer" , "Reverberate - nymph spurned by Narcissus" , "Noise heard again" .)