What does Boxing Day have to do with boxing?
late 14c., from Late Latin confoederatus "leagued together," past participle of confoederare "to unite by a league," from com- "with, together" (see com-) + foederare, from foedus (genitive foederis) "a league" (see federal). Also used as a past participle adjective from late 14c., as a simple adjective from 1550s; meaning "of or belonging to the Confederate States of America" is from 1861. Used as a noun from late 15c. (Late Latin confoederatus also was used as a noun in its day).
A descriptive term for the institutions and people of the Confederacy.