Plantation area run well by corporation (9)
I believe the answer is:
arboretum
'plantation' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'area run well by corporation' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'run' becomes 'r' (cricket abbreviation).
'well by' becomes 'bore' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'corporation' becomes 'tum' ('corporation' is a humorous term for stomach fat).
'a'+'r'+'bore'+'tum'='ARBORETUM'
Can you help me to learn more?
(Other definitions for arboretum that I've seen before include "Botanic garden of trees" , "Collection of elders, say" , "Garden where trees and shrubs are cultivated" , "there's high growth" , "Botanical tree garden" .)