Twin in Genesis (4)
I believe the answer is:
esau
'twin in genesis' 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 "man tricked by kid brother" , "He gave away his biblical birthright for a mess of pottage" , "Son of Isaac and Rebecca" , "Jacob's brother (Gen.)" , "Elder of the twin sons of Isaac and Rebecca" .)