Le billet doux ou la lettre d’amour (circa 1775), by Jean-Honoré Fragonard (1732-1806)
source: Wikimedia Commons/The Metropolitan Museum of Art, New York
a love letter
It is a borrowing from the French noun poulet, literally chicken and chicken meat, used figuratively in the sense of written message in Le Pelerinage de mariage, a farce dating back to 1556:
Voecy un terible poullaict (This is a terrible poulet)
The word was first used in the sense of love letter by Michel de Montaigne (1533-92) in the 1588 edition of his Essais:
(1842 edition of the 1686 translation by Charles Cotton (1630-87)):
Of the same sheet of paper whereon the judge has but just written a sentence against an adulterer, he steals a piece whereon to write a love-letter to his companion’s wife.
original text (Villey-Saulnier edition):
De ce mesme papier où il vient d’escrire l’arrest de condemnation contre un adultere, le juge en desrobe un lopin pour en faire un poulet à la femme de son compaignon.
The origin of this transferred use is unclear. It perhaps arose from the fact that when folding these messages, one would make two tips resembling chicken wings. This seems to be supported by the following from L’École des maris (The School for Husbands, a comedy first performed in 1661), by the French playwright and actor Molière (Jean-Baptiste Poquelin, 1622-73):
I saw a young man at yonder turning, who first came, most unexpectedly, to wish me good morning, on the part of this impertinent man, and then threw right into my chamber a box, enclosing a sealed letter in (the form of a) chicken.
French text (1819 edition):
J’ai vu dans ce détour un jeune homme paroître,
Qui d’abord, de la part de cet impertinent,
Est venu me donner un bonjour surprenant,
Et m’a, droit dans ma chambre, une boîte jetée
Qui renferme une lettre en poulet cachetée.
The first known instance of the figurative use in English is from A Dialogue between Dr. Sherlock, the King of France, the great Turk, and Dr. Oates (1691), by the Church of England clergyman and religious controversialist William Sherlock (died 1707):
Dr. Sherlock. I’le undertake to make Captain Tom, the most Dreadful, the most Soveraign, and the most Divine Thing upon Earth.
Dr. Oates. I would only know which way you would confer that Power upon him; for why should not I convey it as well as you? Will you send it in a Basket as a Token of your pure Love to absolute Soveraignty, or in a Billet Dieu [sic], or in a Poulet as I us’d to do to the Nuns at Salamanca?