harbour vs port of call

harbour and port of call both are nouns.

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

As nouns, port of call is a hyponym of harbour; that is, port of call is a word with a more specific, narrower meaning than harbour:

Other hyponyms of harbour include coaling station.

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

harbour (verb)	port of call (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)