hack driver vs taxidriver

hack driver and taxidriver both are nouns.

Word	Noun	Adjective	Verb	Adverb
hack driver	Yes	No	No	No
taxidriver	Yes	No	No	No

As nouns, hack driver and taxidriver are synonyms defined as:

Other synonyms of hack driver include cabby, cabdriver, cabman, hack-driver, livery driver, taximan.

hack driver (noun)	taxidriver (noun)
someone who drives a taxi for a living	someone who drives a taxi for a living