rack up vs walk

rack up is not a noun while walk is a noun.

Word	Noun	Adjective	Verb	Adverb
rack up	No	No	Yes	No
walk	Yes	No	Yes	No

As verbs, walk is a hyponym of rack up; that is, walk is a word with a more specific, narrower meaning than rack up:

Other hyponyms of rack up include par, shoot, convert, homer, kick, eagle, hole up, ace, equalise, equalize, get even, get, have, make.

rack up (noun)	walk (noun)
	the act of traveling by foot
	(baseball) an advance to first base by a batter who receives four balls
	a slow gait of a horse in which two feet are always on the ground
	the act of walking somewhere
	careers in general
	a path set aside for walking
	manner of walking

rack up (verb)	walk (verb)
supply a rack with feed for (horses or other animals)	obtain a base on balls
defeat thoroughly	give a base on balls to
gain points in a game	use one's feet to advance; advance by steps
place in a rack	accompany or escort
	walk at a pace
	traverse or cover by walking
	take a walk; go for a walk; walk for pleasure
	make walk
	live or behave in a specified manner
	be or act in association with