a game of chance, in which a small ball is made to move round rapidly on a circle divided off into numbered red and black spaces, the one on which it stops indicating the result of a variety of wagers permitted by the game.-a small toothed wheel used by engravers to roll over a plate in order to order to produce rows of dots.-a similar wheel used to roughen the surface of a plate, as in making alterations in a mezzotint.-the curve traced by any point in the plane of a given curve when the latter rolls, without sliding, over another fixed curve. see cycloid, and epycycloid.