What does Boxing Day have to do with boxing?
late 14c., from Old French exempt (13c.) and directly from Latin exemptus, past participle of eximere "remove, take out, take away; free, release, deliver, make an exception of," from ex- "out" (see ex-) + emere "buy," originally "take," from PIE root *em- "to take, distribute" (cf. Latin sumere "to take, obtain, buy," Old Church Slavonic imo "to take," Lithuanian imui, Sanskrit yamati "holds, subdues"). For sense shift from "take" to "buy," compare Old English sellan "to give," source of Modern English sell "to give in exchange for money;" Hebrew laqah "he bought," originally "he took;" and colloquial English I'll take it for "I'll buy it."
mid-15c., from Middle French exempter, from exempt (adj.); see exempt (adj.). Related: Exempted; exempting.