Billet-doux (4,6)
I believe the answer is:
love letter
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">billet-doux</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 love letter that I've seen before include "romantic reading material" , "Billet-doux" , "caring note!" .)