Duck? Eager to eat it! (5)
I believe the answer is:
avoid
'duck?' is the definition.
(duck can mean to avoid)
'eager to eat it' is the wordplay.
'eager' becomes 'avid' (synonyms).
'to eat' indicates putting letters inside.
'it' becomes 'o' (I can't justify this - if you can you should give a lot more credence to this answer).
'avid' enclosing 'o' is 'AVOID'.
Can you help me to learn more?
(Other definitions for avoid that I've seen before include "Steer clear of, dodge" , "Desist" , "Keep away from (someone/something)" , "(If you can't 10), keep away from" , "Bypass" .)