express emotion vs keen

express emotion is not a noun while keen is a noun.

Word	Noun	Adjective	Verb	Adverb
express emotion	No	No	Yes	No
keen	Yes	Yes	Yes	No

As verbs, keen is a hyponym of express emotion; that is, keen is a word with a more specific, narrower meaning than express emotion:

Other hyponyms of express emotion include express joy, express mirth, laugh, cry, weep, break, burst, erupt, lament.

express emotion (noun)	keen (noun)
	a funeral lament sung with loud wailing

express emotion (adjective)	keen (adjective)
	excellent
	intense or sharp
	having or demonstrating ability to recognize or draw fine distinctions
	having a sharp cutting edge or point
	painful as if caused by a sharp instrument

express emotion (verb)	keen (verb)
give verbal or other expression to one's feelings	express grief verbally