Grain, making excellent return after organised coup, in plentiful supply (10)
I believe the answer is:
cornucopia
'plentiful supply' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'grain making excellent return after organised coup' is the wordplay.
'grain making' becomes 'corn' (I can't explain this - if you can you should give a lot more credence to this answer).
'excellent' becomes 'ai' (resembles 'Ac', old-fashioned term for excellent).
'return' shows that the letters should be reversed in order.
'after' is a charade indicator (letters next to each other).
'organised' is an anagram indicator.
'ai' in reverse letter order is 'ia'.
'coup' is an anagram of 'ucop'.
'ia' put after 'ucop' is 'ucopia'.
'corn'+'ucopia'='CORNUCOPIA'
'in' is the link.
Can you help me to learn more?
(Other definitions for cornucopia that I've seen before include "Wealth" , "Great abundance" , "mine" , "Abundant supply of good things" , "Horn of plenty" .)