Is it ensure, insure, or assure?
British billiards game in which each player uses a cue ball of a different colour and tries to pocket the ball of a particular opponent, thus taking a "life." Players have three lives and pay into a betting pool at the start of the game. The last player with a life wins the pool. During play, a player who takes a life wins a stake from that opponent. There are also a number of other forfeits paid into the pool for such errors as pocketing one's own ball or knocking a ball off the table. Pool was a forerunner of the game snooker.