Advise of danger (4)
I believe the answer is:
warn
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">advise of danger</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 warn that I've seen before include "Alert" , "Give advance notice to" , "Notify in advance of danger" , "Sound the alarm" , "Tip off" .)