This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. An optical instrument used for seeing inside tight spaces, consisting of a rigid or flexible tube with an optical relay inside so that the view through a lens or window at one end of the tube may be seen from a lens or eyepiece in the opposite end of the tube.

"I would try another scope known to be good to go, remount tightly, borescope, get it on paper at 50 yards and check your groups. if you can't get them to damn near cloverleaf at 50, ask someone else to try it."

endoscope    periscope