What does Boxing Day have to do with boxing?
mid-14c., from Old French incurable (13c.), from Late Latin incurabilis, from in- "not" (see in- (1)) + curabilis "curable" (see curable). Related: Incurably.
incurable in·cur·a·ble (ĭn-kyur'ə-bəl)adj. Being such that a cure is impossible; not curable.