Any of various tubular optical instruments that contain reflecting elements, such as mirrors and prisms, to permit observation from a position displaced from a direct line of sight.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "periscope" in a sentence
"The periscope is turned on and you are able to view the outside by clicing on the lense."
"How the levers on the right side of the periscope is placed decide what you see outside."
"The company's Barrington, N.J., showroom burgeoned with government-surplus supplies, an array of telescopes and a functioning 38-foot periscope from a Japanese submarine."