Hebrew, “Lights and Perfections.” A holy or sacred device for divination, cleromancy, and divining oracles. They were used by the High Priest and High Priestesses to answer a question or reveal the will of God. Some scholars believe that this refers to two objects used to answer yes or no questions.
The meaning of these terms is uncertain, possibly Urim from the root word “Lights” and Thummim from the root “Innocents,” generally taken to mean “Perfections.” The terms together may also mean “revelation and truth.” The Urim and Thummim are mentioned in the Hebrew Bible as a part of the breastplate worn by the High Priest. In the plates of brass, they are also worn by the High Priestesses. They were believed to be used for divination and cleromancy.
The urim and thummim of Abraham and of the Nephites may not be the same type of urim and thummim used by the Levite Priests and Priestesses. The Urim and Thummim used to divine the translation of the lost 116 pages of Book of Lehi were not identical to the Urim and Thummim of the Old Testament. According to page 101 of Lucy Mack Smith, mother or Joseph Smith Jr.’s 1853 “Biographical sketches of Joseph Smith the prophet, and his progenitors for many generations” they were “two smooth three-cornered diamonds.” These “diamonds” were said to have been placed in silver bows that were fastened to a breastplate.
In the Latter Day Saint movement, Urim and Thummim may also refer to a seer stone, something similar to the rock Joseph Smith Jr. placed in a hat to translate the Book of Mormon. The “Urim and Thummim” actually used to divine the translation of the Book of Mormon available to readers today was given to Joseph Smith Jr. by placing his brown seer stone into a hat. This is clearly different from the bow attaching glasses to a chest plate kept with the gold plates and what is described in the Old Testament and the plates of brass.
See 1 Moses 23:5-8, 26:21; 3 Moses 38:34, 57:8; 4 Moses 30:8; Exodus 28:30; Leviticus 8:8; Numbers 27:21; Deuteronomy 33:8; Melchizedek 6:3-4; Zenos 2:8, 6:8; Ezra 2:63; Mosiah 5:72-75, 8:13 OPV; Ether 1:88-93 RAV, 3:23-28 OPV; Avahr 7:34, 24:28, 39:2, Seer Stone.