Eve's eldest (4)
I believe the answer is:
cain
'eve's eldest' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cain that I've seen before include "Slayer of Abel" , "Brother of Abel" , "First person born in Bible" , "Eldest son of Adam, Eve" , "First murderer reported in the Bible" .)