1610s as the name of an Italian and Turkish gold coin, from French sequin (17c.), from Italian zecchino, the name of a gold coin minted by the Venetian Republic, from zecca "a mint" (13c.), which is from Arabic sikka "a minting die," hence, by extension, "coined money, coinage."
The meaning "ornamental disc or spangle" is by 1852 in fashion articles, also in descriptions of the attire of women in the Orient, who wore the Venetian coins perforated as earrings or necklaces. The Ladies' Department of "The Genesee Farmer" reports in November 1865 that "Head dresses are all in the Greek style, either fillets of velvet studded with beads, or stars of gilt silver, silver, or steel, or else they are hung with chains of gilt sequins." The past-participle adjective sequined is by 1889.