What does Boxing Day have to do with boxing?
1560s, "channelled, fluted," from the verb form of chamfer (v.); see chamfer (n.)). Meaning "bevelled off" is from c.1790.
c.1600, "small groove cut in wood or stone," from Middle French chanfraindre (15c., Modern French chanfreiner), past participle of chanfraint. The second element seems to be from Latin frangere "to break" (see fraction); perhaps the whole word is cantum frangere "to break the edge." Meaning "bevelled surface of a square edge or corner" is attested from c.1840, of uncertain connection to the other sense.