Croon (4)
I believe the answer is:
sing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">croon</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 sing that I've seen before include "Chant" , "Act as informer" , "Inform - carol" , "Croon" , "Warble" .)