Area of land indeed has diminished (9)
I believe the answer is:
detracted
'diminished' is the definition.
Although both the answer and definition are past participle verbs, I don't understand how they can define each other.
'area of land indeed' is the wordplay.
I cannot quite see how this works, but
'area' could be 'tract' (tract is a kind of area) and 'tract' is found within the answer.
The remaining letters 'deed' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'has' is the link.
Can you help me to learn more?
(Other definitions for detracted that I've seen before include "Diminished worth" , "Took away" , "taken away" .)