bus driver vs driver

bus driver and driver both are nouns.

Word	Noun	Adjective	Verb	Adverb
bus driver	Yes	No	No	No
driver	Yes	No	No	No

As nouns, driver is a hypernym of bus driver; that is, driver is a word with a broader meaning than bus driver:

bus driver (noun)	driver (noun)
someone who drives a bus	a golf club (a wood) with a near vertical face that is used for hitting long shots from the tee
	(computer science) a program that determines how a computer will communicate with a peripheral device
	the operator of a motor vehicle
	a golfer who hits the golf ball with a driver
	someone who drives animals that pull a vehicle