Hear this from ass hacking across English hectares (9)
I believe the answer is:
'hear this from ass' is the definition.
The definition suggests a singular noun but the answer is not.
'hacking across english hectares' is the wordplay.
'hacking' becomes 'hewing'.
'across' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'hectares' becomes 'ha' (abbreviation for hectares).
'hewing' going around 'eha' is 'HEEHAWING'.