The Collaborative International Dictionary
Polyoptrum
Polyoptron \Pol`y*op"tron\, Polyoptrum \Pol`y*op"trum\, n. [NL., from Gr. poly`s many + ? seen.] (Opt.) A glass through which objects appear multiplied, but diminished in size. [R.]
Wiktionary
polyoptrum
n. (context dated English) A glass through which objects appear multiplied, but diminished in size.