Son of Isaac (4)
I believe the answer is:
'son of isaac' is the definition.
(I know that Esau father Isaac)
This is the entire clue.
(Other definitions for esau that I've seen before include "Jacob's brother (OT)" , "Birthright seller (Bible)" , "First son of Isaac (Bible)" , "Rebecca's son" , "Biblical character sounds as if he had a vision" .)