Engine (5)
I believe the answer is:
motor
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">engine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for motor that I've seen before include "Engine of vehicle" , "Travel by car, engine" , "Engine - relating to movement" , "Make good progress" , "(Transport using) engine" .)