Nymph Echo stops wolf perhaps going after duck (7)
I believe the answer is:
oceanid
'nymph' is the definition.
(I know that Oceanid is a type of sea nymph)
'echo stops wolf perhaps going after duck' is the wordplay.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'stops' indicates putting letters inside (stopping can mean blocking a gap).
'wolf perhaps' becomes 'canid' (wolf is a kind of canid).
'going after' is a charade indicator (letters next to each other).
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'e' placed into 'canid' is 'ceanid'.
'ceanid' put after 'o' is 'OCEANID'.
(Other definitions for oceanid that I've seen before include "Creature of the deep" , "Water nymph, child of Titans" , "Sea nymph" .)