220 yards (7)
I believe the answer is:
furlong
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">220 yards</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for furlong that I've seen before include "Measure of length" , "One-eight of a mile" , "Measure of distance" , "220 yards" , "One eighth of a mile" .)