periscope Syllabification: (per·i·scope)Pronunciation: /ˈperəˌskōp/Translate periscope | into French | into German | into Italian | into Spanish Definition of periscope noun an apparatus consisting of a tube attached to a set of mirrors or prisms, by which an observer (typically in a submerged submarine or behind a high obstacle) can see things that are otherwise out of sight. periscope in other Oxford dictionaries Definition of periscope in the British & World English dictionary