What does Boxing Day have to do with boxing?
early 14c., from Old French lintel "threshold" (13c., Modern French linteau), of uncertain origin, probably a variant of lintier, from Vulgar Latin *limitaris "threshold," from Latin limitaris (adj.) "that is on the border," from limes (genitive limitis) "border, boundary" (see limit (n.)). Altered by influence of Latin limen "threshold."
(1.) Heb. mashkoph, a projecting cover (Ex. 12:22, 23; ver. 7, "upper door post," but R.V. "lintel"); the head-piece of a door, which the Israelites were commanded to mark with the blood of the paschal lamb. (2.) Heb. kaphtar. Amos 9:1; Zeph. 2:14 (R.V. correctly "chapiters," as in A.V. marg.).