A tube with mirrors that lets you see over or around objects without being seen, commonly used in submarines.
From Greek 'peri-' meaning around and 'skopeein' meaning to look or examine. The device was invented in the early 1900s and the word was created from these Greek roots.
Submarines used periscopes for over a century before modern electronic cameras made them almost obsolete, yet the word lives on. Kids still play 'periscope' games, and now the word names an app for live video—showing how a 100-year-old invention influenced modern technology naming.
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