cheer up vs cheer

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

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

As verbs, cheer up and cheer are synonyms defined as:

Other synonyms of cheer up include chirk up.

As verbs, cheer up and cheer are synonyms defined as:

Other synonyms of cheer up include jolly along, jolly up.

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

cheer up (verb)	cheer (verb)
become cheerful	become cheerful
cause (somebody) to feel happier or more 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