Completely right to eat for example nothing in fast (7)
I believe the answer is:
allegro
'fast' is the definition.
(similar in meaning)
'completely right to eat for example nothing' is the wordplay.
'completely' becomes 'all' (synonyms).
'right' becomes 'r' (abbreviation).
'to eat' means one lot of letters goes inside another (word on the right has word on the left to eat).
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'nothing' becomes 'O' (looks like zero - 0).
'eg'+'o'='ego'
'r' inserted into 'ego' is 'egro'.
'all'+'egro'='ALLEGRO'
'in' acts as a link.
(Other definitions for allegro that I've seen before include "Lively, quick (mus.)" , "In rapid tempo" , "Brisk musical piece" , "Scored at a brisk speed" , "In quick time" .)