Cain's eldest (5)
I believe the answer is:
enoch
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cain's eldest</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for enoch that I've seen before include "Man in Bible" , "___ Powell, Tory politician, d. 1998" , "Father of Methuselah" , "Cain's eldest son - Methuselah's father" , "Oldest city father" .)