Gnat, for one (4)
I believe the answer is:
pest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gnat for one</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 pest that I've seen before include "Destructive insect or other animal" , "Annoying thing" , "Troublesome person" , "Annoying nuisance" , "Constant nuisance" .)