Stair (4)

I believe the answer is:
step
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stair</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for step that I've seen before include "Put foot on a pest" , "Stride" , "Second half of quick 20?" , "Part of a stairway" , "Pest (anag.)" .)