Helicopter part (5)
I believe the answer is:
rotor
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">helicopter part</span>' is the definition.<br/ ><span class="explanation-format__explanation">('rotor' is part of 'helicopter')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rotor that I've seen before include "Turning part of a mechanism" , "Mechanical part that revolves, an acronym" , "Revolving arm in machine" , "Revolving blade (as on helicopter)" , "Mechanical turning part" .)