Biblical divinity cut grass back (6)
I believe the answer is:
yahweh
'biblical divinity' is the definition.
(Hebrew name for God in the Bible)
'cut grass back' is the wordplay.
'cut' becomes 'hew' (hew can mean to chop or cut).
'grass' becomes 'hay' (hay is dried grass).
'back' is a reversal indicator.
'hew'+'hay'='hewhay'
'hewhay' reversed gives 'YAHWEH'.
(Other definitions for yahweh that I've seen before include "Jehovah" , "A name for the God of the Old Testament" , "God (OT)" .)