Brother in "Am I my brother's keeper?" (4)
I believe the answer is:
abel
'brother in am i my brother's keeper?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abel that I've seen before include "One man was murdered" , "Cain's victim; - Magwitch (Great Expectations)" , "fellow killed by brother" , "One of the first children" , "Early murder victim" .)