Stopwatch (5)
I believe the answer is:
timer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stopwatch</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 timer that I've seen before include "chronometer" , "Recorder of duration" , "hourglass" , "Maybe watch" , "Stopwatch, say" .)