Revolving machine part (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">revolving machine part</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 rotor that I've seen before include "Revolving part of machinery" , "Revolving mechanism" , "Reversible piece of moving machinery?" , "Rotating part of machine" , "Revolving blade (as on helicopter)" .)