Source : Webster's Revised Unabridged Dictionary (1913)

Polemoscope \Po*lem"o*scope\, n. [Gr. ? war + -scope: cf. F.
   pol['e]moscope.]
   An opera glass or field glass with an oblique mirror arranged
   for seeing objects do not lie directly before the eye; --
   called also {diagonal, or side, opera glass}.