sub vs periscope

sub and periscope both are nouns.

Word	Noun	Adjective	Verb	Adverb
sub	Yes	No	Yes	No
periscope	Yes	No	No	No

sub (noun)	periscope (noun)
a submersible warship usually armed with torpedoes	an optical instrument that provides a view of an otherwise obstructed field
a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States

sub (verb)	periscope (verb)
be a substitute