An optical instrument that provides a view of an otherwise obstructed field.

Roget 441: vision, sight, optics, eyesight.    view, look, espial^†, glance, ken [Scot.], coup d'oeil [Fr.]; glimpse, glint, peep; gaze, stare, leer; perlustration^†, contemplation; conspection^†, conspectuity^†; regard, survey; introspection; reconnaissance, speculation, watch, espionage, espionnage [Fr.], autopsy; ocular inspection, ocular demonstration; sight-seeing.    point of view; gazebo, loophole, belvedere, watchtower.    field of view; theater, amphitheater, arena, vista, horizon; commanding view, bird's eye view; periscope.    visual organ, organ of vision; eye; naked eye, unassisted eye; retina, pupil, iris, cornea, white; optics, orbs; saucer eyes, goggle eyes, gooseberry eyes.    short sight etc. 443; clear sight, sharp sight, quick sight, eagle sight, piercing sight, penetrating sight, clear glance, sharp glance, quick glance, eagle glance, piercing glance, penetrating glance, clear eye, sharp eye, quick eye, eagle eye, piercing eye, penetrating eye; perspicacity, discernment; catopsis^†.    eagle, hawk; cat, lynx; Argus^†.    evil eye; basilisk, cockatrice [Myth.].    ... show more

Dutch: periscoop
Polish: peryskop