R.S.V.P. is an initialism from French répondez s’il vous plaît (literally respond if you please), meaning please reply, used at the end of invitations to request a response.
It first appeared in English in the early 19th century, for example in Domestic Duties; or, Instructions to young married ladies, on the management of their households and the regulation of their conduct in the various relations and duties of married life (London, 1825), by ‘Mrs. William Parkes’ (Frances Byerley Parkes – 1786-1842):
Mrs. L.—How long before a ball is given should the invitations be issued?
Mrs. B.—A month at least, or even six weeks; and the invitation (printed from a copper-plate on cards) is usually either in this form, or in the one that follows:
Mrs. T——— and Family.
Mrs. S. ——
Tuesday, the 27th June.
Requests the honour of Mr. and Mrs. N.’s
Company at a Quadrille Party,
on the 15th of April.
R. S. V. P.
The use of R.S.V.P. in Britain had been evoked by the French writer Pierre-Jean-Baptiste Nougaret (1742-1823) in Londres, la cour et les provinces d’Angleterre, d’Écosse et d’Irlande, ou esprit, mœurs, coutumes, habitudes privées des habitans [sic] de la Grande-Bretagne (London, the court and the provinces of England, Scotland and Ireland, or spirit, mores, customs, private practices of the inhabitants of Great Britain – Paris, 1816):
It is the custom among persons of the first rank in London to add to the bottom of their invitation cards the four initials R. S. V. P. Some persons to whom these cards are addressed absolutely ignore what these letters signify. The wife of a knight baronet who often received such cards, most puzzled by the meaning of these irritating capitals, insistently asked her husband for it, which he was mortified not to be able to give. She sent for her son, who, passing for a prodigy in his college, was very humiliated at not to being able to guess the sense of these mysterious letters; nevertheless, trying to remember everything similar he had seen in his books, he concluded that R. S. meant Romanus Senatus and V. P. Vox Populi, although he could not understand what could have in common the Roman Senate and the people’s voice with an invitation to play cards or to have tea. There was eventually a lady clever enough to get milady out of her predicament, by explaining to her that these four letters were the initials of the four French words, Réponse [= response] s’il vous plaît.
Il est d’usage à Londres, parmi les personnes du premier rang, d’ajouter au bas de leurs cartes d’invitation les quatre lettres initiales : R. S. V. P. Quelques personnes à qui ces cartes sont adressées, ignorent absolument ce que signifient ces lettres. La femme d’un chevalier baronnet qui en recevait souvent de pareilles, fort intriguée de ne pas entendre la signification de ces majuscules désolantes, la demanda avec instance à son mari, qui eut la mortification de ne pouvoir la lui donner. Elle fit appeler son fils, qui, passant dans son collège pour un prodige, fut très humilié de ne pouvoir point deviner le sens de ces lettres mystérieuses ; cependant, cherchant à se rappeler tout ce qu’il avait vu de semblable dans ses livres, il conclut que R. S. signifiait Romanus Senatus, et V. P. Vox populi, quoiqu’il ne pût pas comprendre ce que pouvait avoir de commun le Sénat romain et la voix du peuple, avec une invitation d’aller jouer aux cartes ou prendre du thé. Il se trouva enfin une dame assez habile pour tirer d’embarras milady, en lui apprenant que ces quatre lettres étaient les lettres initiales des quatre mots français, Réponse s’il vous plaît.
Henry Angelo (1760-1839) told a similar story in Angelo’s Pic Nic; or, Table Talk, including numerous recollections of public characters, who have figured in some part or another of the stage of life for the last fifty years (London, 1834):
R. S. AND P.
When Sir —— was introduced to the honours of the metropolitan shreivalty [= shrievalty] and of knighthood, he became drawn out of that close application to business to which he had laudably devoted his earliest days. The first fashionable invitation he received, was from Lady B——, a civic dame, the wife of a former sheriff. It was to an “At Home;” and at nine o’clock, Sir —— waited on my lady, to express his regret that he could not attend the invitation. “I need not tell you, my lady (said the knight), that business must be attended to, before anything else. We have a large order to pack up, which I fear will not be done before half-past nine o’clock, so you see I should be half an hour too late for your party; but I’ve brought the ticket back, that you may scratch out my name, and then it will do for another. Now, my lady, I hope you will excuse me, but do tell me the meaning of this word in the corner, it has puzzled us all at our house exceedingly—R. S. V. P.; my mother says it is a French word, but I think it no word at all. I think it is what they call initials, ‘a Regular Small Whist Party.’ Now tell me, Lady B——, which of us is right?”