hack driver vs livery driver

hack driver and livery driver both are nouns.

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

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

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

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