Jacob's biblical twin (4)
I believe the answer is:
esau
'jacob's biblical twin' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for esau that I've seen before include "One of Isaac's sons" , "First son of Isaac (Bible)" , "Jacob's twin (Bible)" , "Would-be fratricide" , "Biblical character sounds as if he had a vision" .)