Definition of eight-ball:
(n) :
(uncountable) A pocket billiards (pool) game played with sixteen balls (a cue ball and fifteen object balls) on a pool table with six pockets.
(n) :
(countable) The billiard ball, almost always black, bearing the number eight.
(n) :
(countable, slang) A portion of cocaine or methamphetamine weighing ¹⁄₈ of an ounce, or 3.5 grams.
(v) :
(pool, transitive) To outplay (an opponent) by potting all one's color balls and then the black (or eight-ball) without the opponent potting a single one.
(n) :
(countable, aviation, slang) A spherical attitude indicator.
(n) :
(countable, broadcasting) A kind of spherical microphone.