Return call? (4)
I believe the answer is:
echo
'return call?' 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 whose love Narcissus spurned" , "Before foxtrot" , "from Brussels?" , "Reflection of sound wave" , "Nymph; E (radio comms.)" .)