Disagree on duck egg producer (5)
I believe the answer is:
ovary
'egg producer' is the definition.
(I've seen this in another clue)
'disagree on duck' is the wordplay.
'disagree' becomes 'vary' (I can't justify this - if you can you should believe this answer much more).
'on' says to put letters next to each other.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'vary' after 'o' is 'OVARY'.
Can you help me to learn more?
(Other definitions for ovary that I've seen before include "Part of flower" , "Female reproductive organ" , "Egg-producing organ" , "Fem. reproductive organ" , "egg supplier" .)