Cat's sound (4)
I believe the answer is:
purr
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cat's sound</span>' is the definition.<br/ ><span class="explanation-format__explanation">(noise made by a cat)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for purr that I've seen before include "Show pleasure" , "Appreciative feline sound" , "Make contented sound like cat" , "Cat's noise" , "Low vibratory sound" .)