A duck lives on fruit (6)
I believe the answer is:
olives
'fruit' is the definition.
'a duck lives on' is the wordplay.
'a duck' becomes 'o' (resembles zero - 'duck' in cricket).
'on' is a charade indicator (letters next to each other).
'o'+'lives'='OLIVES'
(Other definitions for olives that I've seen before include "Yellowish green fruits" , "Trees grown for their oil-producing fruit" , "'Oddly, I loves these fruits (6)'" , "Fruits from the tree of peace" , "Small green stone fruits, nice in cocktails" .)