All wanting a ring to copy (4)
I believe the answer is:
echo
'to copy' is the definition.
(echo can mean a copy or duplication)
'all wanting a ring' is the wordplay.
'all' becomes 'each' (similar in meaning).
'wanting' indicates named letters should be taken away (to want something can mean to lack it or need it).
'ring' becomes 'O' (letter resembling a ring).
'each' with 'a' removed is 'ech'.
'ech'+'o'='ECHO'
(Other definitions for echo that I've seen before include "Repetition by reflection" , "Rebounding sound" , "repetitive" , "Bounced sound" , "Greek nymph, spurned by Narcissus, who pined away until only her voice remained" .)