What does Boxing Day have to do with boxing?
1590s, "elegance, stylishness," from Middle French garbe "graceful outline" (Modern French galbe), from Italian garbo "grace, elegance," perhaps from Germanic (cf. Old High German gar(a)wi "dress, equipment, preparation;" see gear). Sense of "fashion of dress" is first attested 1620s.
1836, from garb (n.). Related: Garbed; garbing.