port of call vs harbour

port of call and harbour both are nouns.

Word	Noun	Adjective	Verb	Adverb
port of call	Yes	No	No	No
harbour	Yes	No	Yes	No

As nouns, harbour is a hypernym of port of call; that is, harbour is a word with a broader meaning than port of call:

Other hypernyms of port of call include harbor, haven, seaport.

port of call (noun)	harbour (noun)
any port where a ship stops except its home port	a place of refuge and comfort and security
	a sheltered port where ships can take on or discharge cargo

port of call (verb)	harbour (verb)
	maintain (a theory, thoughts, or feelings)
	hold back a thought or feeling about
	keep in one's possession; of animals
	secretly shelter (as of fugitives or criminals)