wharf rat vs Norway rat

wharf rat and Norway rat both are nouns.

Word	Noun	Adjective	Verb	Adverb
wharf rat	Yes	No	No	No
Norway rat	Yes	No	No	No

As nouns, Norway rat is a hypernym of wharf rat; that is, Norway rat is a word with a broader meaning than wharf rat:

Other hypernyms of wharf rat include brown rat, Rattus norvegicus.

wharf rat (noun)	Norway rat (noun)
brown rat that infests wharves	common domestic rat; serious pest worldwide
someone who lives near wharves and lives by pilfering from ships or warehouses