What does Boxing Day have to do with boxing?
c.1200, from Old French chartre (12c.) "charter, letter, document, covenant," from Latin chartula, literally "little paper," diminutive of charta, carta "paper, document" (see chart (n.)).
early 15c., "provide with a charter," from charter (n.). Meaning "to hire" is attested from 1806. Related: Chartered; chartering.