Radar reflection (4)
I believe the answer is:
echo
'radar reflection' 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 "Reflect sound" , "Comms code word for E" , "She loved Narcissus - it's recalled" , "Marked by heat" , "Nymph whose love Narcissus spurned" .)