prop. n. A brand name for a transparent plastic based on methyl methacrylate esters; the term is often used generically to refer to any similar transparent plastic. It is sold in various forms, including rigid sheets which may be used as a substitute for glass in windows. [ Trademark ] [ PJC ]

n. [ See Pollux, and 4th Castor. ] (Min.) A colorless transparent mineral, resembling quartz, occurring with castor or castorite on the island of Elba. It is a silicate of alumina and cæsia. Called also pollux. [ 1913 Webster ]