A low (3)
I believe the answer is:
moo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a low</span>' is the definition.<br/ ><span class="explanation-format__explanation">(both can mean to make the noise of a cow)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for moo that I've seen before include "Irritating woman" , "Cartoon sound of a cow" , "Cow's low" , "unpopular woman" , "Low (of cattle)" .)