Billiard
来自Big Physics
late 16th century: from French billard, denoting both the game and the cue, diminutive of bille (see billet2).
wiktionary
billiard (plural billiards)
From French billiard, equivalent to bi-(“two”) + -illiard.
etymonline
billiard
singular of billiards, used only in combinations (such as billiard-ball, 1630s, billiard-table 1640s).