What is the X in X-mas?
Old English fingor, from Proto-Germanic *fingraz (cf. Old Saxon fingar, Old Frisian finger, Old Norse fingr, Dutch vinger, German Finger, Gothic figgrs), with no cognates outside Germanic; perhaps connected with PIE *penkwe-, the root meaning "five."
As a unit of measure (Middle English) it represents the breadth of a finger, about three-quarters of an inch. They generally are numbered from the thumb, and named index finger, fool's finger, leech- or physic-finger, and ear-finger.
finger fin·ger (fĭng'gər)
One of the five digits of the hand, especially one other than the thumb.
butterfingers, five fingers, give five fingers to, give someone the finger, not lay a glove on someone, play stinky-pinky, put one's finger on something, put the finger on someone, stand around with one's finger up one's ass