What does Boxing Day have to do with boxing?
"clear, open space in a woods," c.1400, perhaps from Middle English glode (c.1300), from Old Norse glaðr "bright" (see glad). Original meaning would be "bright (because open) space in a wood" (cf. French clairière "glade," from clair "clear, bright;" German Lichtung "clearing, glade," from Licht "light"). American English sense of "marshy grassland" (e.g. Everglades) first recorded c.1796.