Prior; ancestor (10)
I believe the answer is:
antecedent
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">prior</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">ancestor</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that ancestor can be written as antecedent)</span><br/ ><br/ ></span>
(Other definitions for antecedent that I've seen before include "Going before (in time/order)" , "Preceding in time or order" , "Something logically preceding another" , "Something existing before another" , "Previous" .)