The Collaborative International Dictionary of English v.0.48:

Sequin \Se"quin\, n. [F. sequin, It. zecchino, from zecca the
   mint, fr. Ar. sekkah, sikkah, a die, a stamp. Cf. Zechin.]
   An old gold coin of Italy and Turkey. It was first struck at
   Venice about the end of the 13th century, and afterward in
   the other Italian cities, and by the Levant trade was
   introduced into Turkey. It is worth about 9s. 3d. sterling,
   or about $2.25. The different kinds vary somewhat in value.
   [Written also chequin, and zequin.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

sequin
    n 1: adornment consisting of a small piece of shiny material
         used to decorate clothing [syn: sequin, spangle,
         diamante]