Big first for a baby (4)
I believe the answer is:
step
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">big first for a baby</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 step that I've seen before include "Pest (anag.)" , "Footprint" , "Stride" , "Dance move" , "Action of the leg" .)