- billet-doux (n.)
[billet-doux 词源字典]
- also billet doux, 1670s, "love letter," French, literally "sweet note," from billet "document, note" (14c., diminutive of bille; see bill (n.1)) + doux "sweet," from Latin dulcis (see dulcet).[billet-doux etymology, billet-doux origin, 英语词源]