Piece of confidential information (3-3)
I believe the answer is:
tip-off
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">piece of confidential information</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tip-off that I've seen before include "Private warning" , "Piece of confidential information" , "Alert" , "Give a secret warning" , "Informed hint" .)