The Collaborative International Dictionary of English v.0.48:

Lotto \Lot"to\ (l[o^]t"t[-o]), n. [F. loto or It. lotto, prop.,
   a lot; of German origin. See Lot.]
   A game of chance, played with cards or tickets, on which are
   inscribed numbers, and any contrivance (as a wheel containing
   numbered balls) for determining a set of numbers by chance.
   The player holding a card having on it the set of numbers
   drawn from the wheel takes the stakes after a certain
   percentage of them has been deducted for the dealer. In some
   systems, lesser prizes are awarded for having some but not
   all of the numbers selected, such as four or five numbers in
   a six-number drawing. A variety of lotto is called keno. In
   another variety, the player chooses the numbers for the card
   or ticket s/he holds. There may be from three to seven
   different numbers on a card or ticket. In a modern
   computerized lotto system conducted by state authorities, the
   player chooses numbers, or allows the computer to choose
   numbers at random, which are then printed on a ticket that
   the player holds until the winning number is selected. [Often
   written loto.]
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

lotto
    n 1: a game in which numbered balls are drawn at random and
         players cover the corresponding numbers on their cards
         [syn: lotto, bingo, beano, keno]