Secretly (3,4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">secretly</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 sub rosa that I've seen before include "Latin phrase for in secrecy or confidence" , "In confidence, beneath nice flower" , "Behind closed doors" , "In strict confidence - in Latin" , "secret" .)