brush up vs retrieve

brush up and retrieve both are verbs.

Word	Noun	Adjective	Verb	Adverb
brush up	No	No	Yes	No
retrieve	No	No	Yes	No

As verbs, retrieve is a hypernym of brush up; that is, retrieve is a word with a broader meaning than brush up:

Other hypernyms of brush up include call back, call up, recall, recollect, remember, think.

brush up (verb)	retrieve (verb)
bring to a highly developed, finished, or refined state	recall knowledge from memory; have a recollection
refresh one's memory	run after, pick up, and bring to the master
	go for and bring back
	get or find back; recover the use of