fill up vs rack up

fill up and rack up both are verbs.

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

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

Other hyponyms of fill up include water, flood.

fill up (verb)	rack up (verb)
make full, also in a metaphorical sense	supply a rack with feed for (horses or other animals)
become full	defeat thoroughly
eat until one is sated	gain points in a game
fill or stop up	place in a rack