The Collaborative International Dictionary of English v.0.48:

Vingt et un \Vingt` et` un"\ [F., twenty and one.]
   A game at cards, played by two or more persons. The fortune
   of each player depends upon obtaining from the dealer such
   cards that the sum of their pips, or spots, is twenty-one, or
   a number near to it; -- also called blackjack, or
   twenty-one.

   Note: There are several variations (such as Caribbean
         blackjack). In the most common variation played in
         casinos, there is one dealer who plays for the house,
         and up to seven players. The players and dealer each
         receive two cards, the dealer's cards usually being one
         face up and one face down. The players each in turn
         decide whether they will request additional cards
         ("hit"), the objective being to reach a sum of card
         values as close as possible to twenty-one, without
         exceeding that number. If, on hitting, the player's
         total card values exceed 21, he has "busted", and lost
         his bet. Otherwise, the player wins only if his total
         card values exceed those of the dealer. "picture cards"
         (or "face cards", being the jack, queen, and king) are
         counted as having a value of ten. The ace may count as
         one or eleven, at the player's option. Other than to
         hit, there are also other possible actions by the
         player, such as to "double down" (receive only one
         additional card, while doubling the initial bet), or to
         "split" (if the first two cards have the same value).
         [1913 Webster +PJC]