cheer up vs buoy up

cheer up and buoy up both are verbs.

Word	Noun	Adjective	Verb	Adverb
cheer up	No	No	Yes	No
buoy up	No	No	Yes	No

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

Other hyponyms of cheer up include exuberate, exult, jubilate, rejoice, triumph, lighten, lighten up.

cheer up (verb)	buoy up (verb)
become cheerful	become more cheerful
cause (somebody) to feel happier or more cheerful	keep afloat
	make more cheerful