busman vs driver

busman and driver both are nouns.

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

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

busman (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