Lock or plait (5)
I believe the answer is:
tress
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">lock</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(both can mean a piece of hair)</span><br/ ><br/ >'<span class="explanation-format__original">plait</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for tress that I've seen before include "Obsolete support" , "Bit of hair" , "Rests (anag.)" , "is a bit of a shock" , "Switch" .)