The Collaborative International Dictionary of English v.0.48:

Urim \U"rim\, n. [Heb. ?r[imac]m, pl. of ?r, fire ?r light.]
   A part or decoration of the breastplate of the high priest
   among the ancient Jews, by which Jehovah revealed his will on
   certain occasions. Its nature has been the subject of
   conflicting conjectures.
   [1913 Webster]

         Thou shall put in the breastplate of judgment the Urim
         and the Thummim.                         --Ex. xxviii.
                                                  30.
   [1913 Webster]

         And when Saul inquired of the Lord, the Lord answered
         him not, neither by dreams, nor by Urim, nor by
         prophets.                                --1 Sam.
                                                  xxviii. 6.
   [1913 Webster]

   Note: Professor Plumptre supposes the Urim to have been a
         clear and colorless stone set in the breastplate of the
         high priest as a symbol of light, answering to the
         mystic scarab in the pectoral plate of the ancient
         Egyptian priests, and that the Thummim was an image
         corresponding to that worn by the priestly judges of
         Egypt as a symbol of truth and purity of motive. By
         gazing steadfastly on these, he may have been thrown
         into a mysterious, half ecstatic state, akin to
         hypnotism, in which he lost all personal consciousness,
         and received a spiritual illumination and insight.
         [1913 Webster]

Easton's 1897 Bible Dictionary:

Urim
   lights (Vulg."doctrina;" LXX. "revelation"). See THUMMIM.


Hitchcock's Bible Names Dictionary (late 1800's):

Urim, lights; fires