Engine booster (5)
I believe the answer is:
turbo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">engine booster</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for turbo that I've seen before include "source of power" , "Charger improves a car's power" , "Engine supercharger" , "found in car" , "Type of supercharger using engines exhaust gases" .)