What does Boxing Day have to do with boxing?
early 13c., "to free from faults, rectify," from Old French amender (12c.), from Latin emendare "to correct, free from fault," from ex- "out" (see ex-) + menda "fault, blemish," from PIE *mend- "physical defect, fault" (cf. Sanskrit minda "physical blemish," Old Irish mennar "stain, blemish," Welsh mann "sign, mark").
Supplanted in senses of "repair, cure" by its shortened offspring mend (v.). Meaning "to add to legislation" (ostensibly to correct or improve it) is recorded from 1777. Related: Amended; amending.