Measure the duration of (4)
I believe the answer is:
time
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">measure the duration of</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for time that I've seen before include "Finite duration" , "weekly magazine" , "The father of Truth, presumably" , "Indefinite period" , "Prison sentence; occasion" .)