livery driver vs hack driver

livery driver and hack driver both are nouns.

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

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

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

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