periscope vs optical instrument

periscope and optical instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
periscope	Yes	No	No	No
optical instrument	Yes	No	No	No

As nouns, optical instrument is a hypernym of periscope; that is, optical instrument is a word with a broader meaning than periscope:

periscope: an optical instrument that provides a view of an otherwise obstructed field
optical instrument: an instrument designed to aid vision

periscope (noun)	optical instrument (noun)
an optical instrument that provides a view of an otherwise obstructed field	an instrument designed to aid vision