Littlest of a litter (4)
I believe the answer is:
runt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">littlest of a litter</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for runt that I've seen before include "little piggy" , "Weak little squealer" , "Litter-weakling" , "Littlest oinker" , "Turn into smallest of the litter" .)