Periscope and Schnorkel

Periscope noun - An optical instrument that provides a view of an otherwise obstructed field.

Schnorkel and periscope are semantically related. In some cases you can replace term "Schnorkel" with "Periscope", this nouns are similar.

Schnorkel noun - Air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time.

Periscope and schnorkel are semantically related. Sometimes you can replace term "Periscope" with "Schnorkel", this nouns are similar.