What does Boxing Day have to do with boxing?
Old English cwicseolfor, literally "living silver," translating Latin argentum vivum (cf. Italian argento vivo), literally "living silver;" so called from its liquid mobility. See quick (adj.) + silver (n.). Cf. Dutch kwikzilver, Old High German quecsilbar, German quecksilber, French vif-argent, Italian argenta viva.