Novelist retaining hard copy (4)
I believe the answer is:
Here is my best explanation:
'copy' is the definition.
'novelist retaining hard' is the subsidiary indication.
'novelist' becomes 'eco' (Umberto Eco).
'retaining' indicates putting letters inside.
'hard' becomes 'h'.
'eco' placed around 'h' is 'echo'.
(Other definitions for echo that I've seen before include "Nymph; E (radio comms.)", "She loved Narcissus - it's recalled", "Noise heard again", "Reflection of sound waves", "Reverberation of sound", "Rebounding sound", "Greek nymph, spurned by Narcissus, who pined away until only her voice remained", "Mimic", "Audio effect" and "Evocation".)