Sentence:  Many sorts of glass were in the market, called Lambeth or Ratcliffe, Normandy, German, white and green, Dutch, Newcastle, Staffordshire, and Bristol glass, <WSD>looking glass</WSD> and jealous glass. ... <WSD>Looking glass</WSD> plates were sometimes used in windows. 
Meaning of the word marked with <WSD> tags:  (t=smooth surface that reflects light so as to give an image of what is in front of it). (from 1520s)