Osentsoir
France, 4e quart du XVe siécle.
Cuivre doré, émaux translucides sur basse-taille, verre
Fonds Du Sommerand, Cl. 992

Which can be roughly translated as:

Monstrance
France, 4th quarter of the 15th Century.
Gilded coper, translucent enamel "basse-taille", glass.
Funds from Sommerand, Cluny catalog number 992

A Osentsoir or Monstrance is not strictly a reliquary, but a device use to display the holy eurcharist (the flat round bread used as a sacrament in Catholic masses to represent the body of Christ). From the latin monstrare, "to show."

Basse-taille (French for "low-cut") is a technique of enamelling in which the metal surface is carved in low relief then covered with a tanslucent enamel. There are some good examples here. It's not too easy to see in this piece, however. Probably it's in the 8 pointed stars 2/3rds of the way down the handle.

More information on reliquaries can be found at Wikipedia and at the Metropolitan Museum of Art site.