Confidentially! (7,3,3,2)
I believe the answer is:
between you and me
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">confidentially</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 between you and me that I've seen before include "Don't tell anybody else!" , "not going any further" , "our inheritance may be so divided" , "Confidentially" , "said in private" .)