My property features open, extensive grounds at the back (8)
I believe the answer is:
goodness
'my' is the definition.
(I've seen this before)
'property features open extensive grounds at the back' is the wordplay.
'property' becomes 'goods' (I can't explain this - if you can you should believe this answer much more).
'features' indicates putting letters inside.
'at the back' indicates one should take the final letters.
The last letters of 'open extensive grounds' are 'nes'.
'goods' enclosing 'nes' is 'GOODNESS'.
Can you help me to learn more?
(Other definitions for goodness that I've seen before include "Morality, generosity, kindness" , "Exclamation of surprise" , "merit" , "Quality of being morally good or virtuous" , "Virtue, righteousness" .)