buck up vs cheer

buck up is not a noun while cheer is a noun.

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

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

Other hypernyms of buck up include embolden, hearten, recreate.

buck up (noun)	cheer (noun)
	the quality of being cheerful and dispelling gloom
	a cry or shout of approval

buck up (verb)	cheer (verb)
gain courage	become cheerful
	spur on or encourage especially by cheers and shouts
	show approval or good wishes by shouting
	cause (somebody) to feel happier or more cheerful
	give encouragement to