A breastplate is a piece of armour that covers and protects the chest.
breastplate in British English
(ˈbrɛstˌpleɪt)
noun
1.
a piece of armour covering the chest
2.
the strap of a harness covering a horse's breast
3. Judaism
an ornamental silver plate hung on the scrolls of the Torah
4. Old Testament
a square vestment ornamented with 12 precious stones, representing the 12 tribes of Israel, worn by the high priest when praying before the holy of holies
5. zoology a nontechnical name for plastron
breastplate in American English
(ˈbrɛstˌpleɪt)
noun
1.
a piece of armor for the breast
2.
in ancient times, an embroidered cloth worn on the breast of the Jewish high priest: it was set with twelve jewels representing the twelve tribes of Israel