One third of a yard (4)
I believe the answer is:
foot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one third of a yard</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for foot that I've seen before include "Unit of length" , "12 inches" , "See 24" , "Labour Party leader, 1980-83" , "Measure - part of body" .)