breastplate

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A piece of armor that covers the breast.
2. n. Judaism A square cloth set with 12 precious stones representing the 12 tribes of Israel, worn over the breast by ancient high priests.

Century Dictionary and Cyclopedia

1. n. A square ornament worn by the Jewish high priest, consisting of the same textile fabric as the ephod, and bearing twelve precious stones engraved with the names of the twelve tribes of Israel, set in the gold. The breastplate was hung by chains of gold to that part of the ephod which was on the shoulder, and the lower side was secured to the girdle by blue laces; for this purpose four rings of gold were secured to the four corners. It was also called the breastplate of judgment, because it contained the Urim and the Thummim.
2. n. The armor for the front of the body, when made in one piece reaching from the waist to about the collar-bone. It was not introduced until a very late period in the his tory of armor, and was not common until the early years of the sixteenth century, when armor for the limbs was being abandoned. See back and breast (under back), corselet, and cuirass.
3. n. A strap that runs across a horse's breast.
4. n. A plate or piece which receives the buttend of a boring-tool, and is held against the breast when the tool is in use. Also called conscience and palette.
5. n. The sternum or central piece on the lower side of the cephalothorax of a spider, between the bases of the legs.
6. n. The lower shell or plastron of a tortoise.
7. n. The iron plate used for covering the breast-hole of a cupola.

Wiktionary

1. n. A piece of armor that covers the chest.
2. n. A piece of horse tack designed to prevent the saddle slipping backwards.

GNU Webster's 1913

1. n. A plate of metal covering the breast as defensive armor.
2. n. A piece against which the workman presses his breast in operating a breast drill, or other similar tool.
3. n. A strap that runs across a horse's breast.
4. n. (Jewish Antiq.) A part of the vestment of the high priest, worn upon the front of the ephod. It was a double piece of richly embroidered stuff, a span square, set with twelve precious stones, on which were engraved the names of the twelve tribes of Israel. See Ephod.

WordNet 3.0

1. n. armor plate that protects the chest; the front part of a cuirass