From BiblePortal Wikipedia

People's Dictionary of the Bible [1]

Looking-glass. This word occurs in  Exodus 38:8;  Job 37:18; also in  Isaiah 3:23, where it is simply "glasses." The R. V. reads mirrors in these three places. The articles intended were mirrors, tablets, or plates of polished metal, mostly of a round form, and furnished with handles. Those carried by the Hebrew women at the time of the construction of the vessels of the tabernacle were used for making "the laver of brass and the foot of it of brass." Many mirrors have been discovered in Egypt, and are to be seen in museums. They are of mixed metal, chiefly copper, very carefully wrought, and highly polished.

Webster's Dictionary [2]

(n.) A mirror made of glass on which has been placed a backing of some reflecting substance, as quicksilver.

Hastings' Dictionary of the Bible [3]

Looking-Glass See Glass.

International Standard Bible Encyclopedia [4]

look´ing - glas (  Exodus 38:8 the King James Version margin "brasen glasses"). See Glass; Mirror .