Definition of nine-ball:
(n) :
The digit or figure 9.
(n) :
(card games) A playing card with nine pips.
(n) :
(baseball) A baseball club, team, or lineup (composed of nine players).
(n) :
(weaponry) A nine-millimeter semi-automatic pistol.
(n) :
(computing, engineering, usually in the plural) A statistical unit of proportion (of reliability, purity, etc.).
(n) :
A surname.