Twist; quirk (4)
I believe the answer is:
kink
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">twist</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that twist can be written as kink)</span><br/ ><br/ >'<span class="explanation-format__original">quirk</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I have seen 'Mental quirk' mean 'kink' so perhaps 'quirk' could also mean 'kink')</span><br/ ><br/ ></span>
(Other definitions for kink that I've seen before include "Eccentricity" , "Sharp bend (in a wire) - quirk" , "Sharp twist in wire or hair, perhaps" , "Idiosyncrasy - sharp bend" , "The whim" .)