wharf rat vs snitcher

wharf rat and snitcher both are nouns.

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

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

wharf rat: someone who lives near wharves and lives by pilfering from ships or warehouses
snitcher: a thief who steals without using violence

Other hypernyms of wharf rat include pilferer, sneak thief.

wharf rat (noun)	snitcher (noun)
brown rat that infests wharves	someone acting as an informer or decoy for the police
someone who lives near wharves and lives by pilfering from ships or warehouses	a thief who steals without using violence