* Noun: A periscope is an optical instrument used for viewing objects that are above the level of sight, typically from a submerged submarine or a trench.
* Verb: To periscope means to use a periscope to look at something. This usage is less common but still valid.
For example:
* Noun: "The submarine used its periscope to locate the enemy ship."
* Verb: "The soldier periscoped over the wall to see what was happening on the other side."