Mirror - Vine's Expository Dictionary of New Testament Words
Mirror[ 1,,G2072, esoptron ]
rendered, glass" in the AV, is used of any surface sufficiently smooth and regular to reflect rays of light uniformly, and thus produce images of objects which actually in front of it appear to the eye as if they were behind it. "Mirrors" in Biblical times were, it seems, metallic; hence the RV adopts the more general term "mirror;" in 1 Corinthians 13:12, spiritual knowledge in this life is represented metaphorically as an image dimly perceived in a "mirror;" in James 1:23, the "law of liberty" is figuratively compared to a "mirror;" the hearer who obeys not is like a person who, having looked into the "mirror," forgets the reflected image after turning away; he who obeys is like one who gazes into the "mirror" and retains in his soul the image of what he should be.
Note: For the verb katoptrizo, "to reflect as a mirror" (some regard it as meaning "beholding in a mirror"), in 2 Corinthians 3:18, See BEHOLD, No. 12.