Accurate timepiece (11)
I believe the answer is:
chronometer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">accurate timepiece</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 chronometer that I've seen before include "Instrument measuring time" , "Accurate timepiece" .)