Definition of "billiard"

A shot in billiards or snooker in which the cue ball strikes two other balls; a carom.  examples

(attributive) Pertaining to the game of billiards.  examples

A dynamical system in which a particle alternates between motion in a straight line and specular reflections from a boundary.  examples

(Britain, rare) 1015, a thousand billion (long scale) or a million milliard.