Mother of Isaac (5)
I believe the answer is:
sarah
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mother of isaac</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sarah that I've seen before include "Lady" , "Abraham's wife (OT)" , "- Bernhardt, Fr. actress" , "Wife of Abraham" , "Girl's name" .)