Definition of "breastplate"

A piece of armor that covers the chest.  examples

A piece of horse tack designed to prevent the saddle slipping backwards.  examples

A piece of silicone in the shape of women's breasts worn by drag queens and other female impersonators to simulate a female body shape.  examples

(Judaism) An embroidered square of linen worn on the breast of the Jewish high priest, bearing twelve precious stones, each inscribed with the name of one of the tribes of Israel.  examples