Extent; duration (6)
I believe the answer is:
length
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">extent</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that length is a type of extent)</span><br/ ><br/ >'<span class="explanation-format__original">duration</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for length that I've seen before include "End-to-end distance" , "Distance from one end of an object to the other" , "A brief swim" , "stretch" , "Measure (to which one should bowl?)" .)