noun a strap that runs across a horse's breast.
2. breastplate ·noun a plate of metal covering the breast as defensive armor.
3. breastplate ·noun a piece against which the workman presses his breast in operating a breast drill, or other similar tool.
4. breastplate ·noun 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.