passenger vs hitchhiker

passenger and hitchhiker both are nouns.

Word	Noun	Adjective	Verb	Adverb
passenger	Yes	No	No	No
hitchhiker	Yes	No	No	No

As nouns, hitchhiker is a hyponym of passenger; that is, hitchhiker is a word with a more specific, narrower meaning than passenger:

passenger: a traveler riding in a vehicle (a boat or bus or car or plane or train etc) who is not operating it
hitchhiker: a person who travels by getting free rides from passing vehicles

Other hyponyms of passenger include commuter, fare, stowaway, straphanger.

passenger (noun)	hitchhiker (noun)
a traveler riding in a vehicle (a boat or bus or car or plane or train etc) who is not operating it	a person who travels by getting free rides from passing vehicles