Speed up (an engine) (3)
I believe the answer is:
rev
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">speed up an engine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rev that I've seen before include "Reverend (abbr.)" , "Minister" , "In engine-room speed up" , "Motor rotation, in short" , "serviceman?" .)