What is the X in X-mas?
children's word to express a claim on something, 1932, originally U.S., apparently a contraction of dibstone "a knucklebone or jack in a children's game" (1690s), of unknown origin.
[perhaps fr dibstones, a children's game played with small bones or other counters]
[probably fr divvy]
game of great antiquity and worldwide distribution, now played with stones, bones, seeds, filled cloth bags, or metal or plastic counters (the jacks), with or without a ball. The name derives from "chackstones"-stones to be tossed. The knuckle, wrist, or ankle bones (astragals) of goats, sheep, or other animals also have been used in play. Such objects have been found in prehistoric caves in Kiev, Ukraine, and pictures of the game are depicted on jars from ancient Greece.