What does Boxing Day have to do with boxing?
late 14c., "place where two things are joined," from Latin iunctura "a joining, uniting, a joint," from iunctus, past participle of iungere "to join" (see jugular). Sense of "point in time" first recorded 1650s, probably from astrology.
juncture junc·ture (jŭngk'chər)
The point, line, or surface of union of two parts.