noun, plural bil·lets-doux [bil-ey-dooz, bil-ee-; French bee-yey-doo] /ˈbɪl eɪˈduz, ˈbɪl i-; French bi yeɪˈdu/.
- a love letter.
noun plural billets-doux (ˌbɪlɪˈduːz, French bijɛdu)
- old-fashioned, or jocular a love letter
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).