Step on a ladder (4)
I believe the answer is:
rung
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">step on a ladder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rung that I've seen before include "Tolled - step on ladder" , "Phoned" , "Level in a hierarchy" , "Step up the ladder - called for" , "Part of a ladder" .)