Biblical patriarch, the son of Abraham (5)
I believe the answer is:
isaac
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">biblical patriarch</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">the son of abraham</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for isaac that I've seen before include "Sarah's son" , "Father to Jacob and Esau" , "- Newton, Eng. physicist and mathematician" , "Father of 21" , "- Asimov, sci-fi writer" .)