"Yes: these four evenings have enabled them to ascertain to they both like Vingt-Un..." (pg. 23)
Vingt-Un is French for "twenty one", the name of the card game. Austen's inclusion of this French term shows that many parts of England were influenced by the Norman invasion more than two hundred years before. French words trickled into the English language, usually as a fancier way of saying a simple English word.