Sudden impulse (4)
(Other definitions for urge that I've seen before include "Encourage to proceed, drive onward" , "Try hard to persuade, advise earnestly" , "Plead" , "Compulsion; egg on" , "Constrain" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden impulse</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 whim that I've seen before include "Urge" , "Caprice, sudden fancy" , "Fad" , "Sudden or capricious idea" , "Fanciful impulse" .)