cheer up vs lighten

cheer up and lighten both are verbs.

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

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

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

cheer up (verb)	lighten (verb)
become cheerful	make more cheerful through the use of color
cause (somebody) to feel happier or more cheerful	become lighter
	alleviate or remove (pressure or stress) or make less oppressive
	become more cheerful
	reduce the weight on; make lighter
	make more cheerful