Relative of Isaac Hayes, cutting grass, needing a uniform (4)
I believe the answer is:
esau
'relative of isaac' is the definition.
(I know that Isaac child Esau)
'hayes cutting grass needing a uniform' is the wordplay.
'cutting' indicates named letters should be taken away.
'grass' becomes 'hay' (hay is dried grass).
'needing' says to put letters next to each other.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'hayes' with 'hay' removed is 'es'.
'es'+'a'+'u'='ESAU'
(Other definitions for esau that I've seen before include "Jacob's twin (Bible)" , "Biblical man who sold his birthright for a mess of pottage" , "Cunning hunter" , "Isaac's eldest son" , "Hairy OT man" .)