What does Boxing Day have to do with boxing?
1610s, name of a former Italian and Turkish gold coin, from French sequin (17c.), from Italian zecchino, name of a Venetian coin, from zecca "a mint," from Arabic sikkah "a minting die." Meaning "ornamental disc or spangle" is first recorded 1882, from resemblance to a gold coin. Related: Sequined (1890).