Highly confidential (3,6)
I believe the answer is:
top secret
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">highly confidential</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 top secret that I've seen before include "As 007 mission" , "label on some classified documents" , "(Of information) strictly not for public consumption" , "restricted" , "Highly classified" .)