Billiard is the form you put in front of another noun: a billiard table, a billiard ball, a billiard cue. The game itself is nearly always called billiards, with an s, like cards or darts. On a cloth-covered table, players hit balls with a long stick (a cue). Learner-dictionary pictures often show pockets at the edge of the table, which is close to what many people call pool. Though actually the English naming is messier than the picture. In the United States, billiards is often the family name for all these table games, and pool is the everyday pocket game. In Britain, billiards can mean a particular older game with three balls (English billiards), while snooker and pool have their own names. Some table games have no pockets at all. Taiwanese students already have 撞球 for the games in a 撞球場; that is the right hook, even if the English labels do not line up one-to-one. Do not say “Let’s play billiard” — that sounds unfinished to most ears. The word came from French billard, which first meant the wooden cue, a little stick, from an older word for a log or tree trunk — not from “two” plus anything.