Ladder step (4)
I believe the answer is:
rung
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ladder step</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 rung that I've seen before include "support for foot" , "Ladder's step" , "Crosspiece of a ladder" , "Tolled - step on ladder" , "Part of a ladder" .)