Nothing eaten by Ovid is egg-shaped (5)
I believe the answer is:
ovoid
'is egg-shaped' is the definition.
(synonyms)
'nothing eaten by ovid' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'eaten by' means one lot of letters goes inside another (inserted letters get eaten).
'o' going within 'ovid' is 'OVOID'.
(Other definitions for ovoid that I've seen before include "rounded shape" , "like eggs!" , "Shaped like an egg" , "Elliptical" , "More or less egg-shaped" .)