Good commission’s collected on fruit (9)
I believe the answer is:
greengage
'good' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'commission's collected on fruit' is the wordplay.
'commission's collected' becomes 'green' (I can't justify this - if you can you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'fruit' becomes 'gage' (a greengage or gage is a type of fruit).
'green'+'gage'='GREENGAGE'
Can you help me to learn more?
(Other definitions for greengage that I've seen before include "Fruit akin to plum" , "Greenish-yellow type of plum" , "Fruit like a small plum" , "Garden fruit" , "Plum-like fruit" .)