‖Bil′let–doux″ (bĭl′lā̍‐do͞o″), n.; pl.Billets-doux (bĭl′lā̍‐do͞oz″). [F. billet note + doux sweet, L. dulcis.] A love letter or note.
A lover chanting out a billet-doux.
Spectator.
Webster's Dictionary 1913
‖Bil′let–doux″ (bĭl′lā̍‐do͞o″), n.; pl.Billets-doux (bĭl′lā̍‐do͞oz″). [F. billet note + doux sweet, L. dulcis.] A love letter or note.
A lover chanting out a billet-doux.
Spectator.