looking glass noun Etymology:looking (gerund of look) (I) + glass 1. a.: a mirror usually made of glass with a backing of some reflecting substance (as mercury) < had first seen her face in the looking glass — Jean Stafford > b.: the glass used in such a mirror < little pieces of looking glass — Leslie Thomas > 2.: something held to resemble or to perform the functions of a looking glass : mirror 1b(1)