BREASTPIECE (BREASTPLATE) OF THE HIGH PRIEST (חֹ֫שֶׁן, H3136, meaning uncertain, LXX λογει̂ον oracle). An elaborately decorated square of linen worn on the breast as part of the robes of Israel’s high priest (Exod 28:15-30; 39:8-21; Lev 8:8). A piece of material of gold, blue, purple, scarlet, and fine linen was folded double into a square of 9x9 inches. It was fastened from the top to the shoulder of the ephod by gold cords, and by a blue lace from the lower corners to gold rings on the ephod. On the front were four rows, each of three precious stones, each stone inscribed with the name of one of the twelve tribes. BDB links חֹ֫שֶׁן, H3136, with a root meaning “beauty,” hence “the chief adornment.” The term “breastplate of judgment” apparently refers to the oracular function of the Urim and the Thummim, commonly thought to have been objects held in the fold. Josephus ascribed the oracular function to the twelve stones. Kalisch and Hertz both argue that the fact that the various descriptions of the breastplate include either the twelve stones or the Urim and the Thummim, but never both together, indicates their identity.
Josephus, Jewish Antiquities III. 7.; M. Kalisch, Exodus (1855), 535-544; J. H. Hertz, The Pentateuch and Haftorahs, II Exodus (1930), 331-336.