Emily Dickinson Lexicon

BREAST'PLATE, n. [breast and plate.]

1. Armor for the breast. – Cowley.
2. A strap that runs across a horse's breast. – Ash.
3. In Jewish antiquity, a part of the vestment of the high priest consisting of a folded piece of the rich embroidered stuff of which the ephod was made. It was set with twelve precious stones, on which were engraved the names of the twelve tribes. – Encyc.