keen vs grieve

keen is a noun but grieve is not a noun.

Word	Noun	Adjective	Verb	Adverb
keen	Yes	Yes	Yes	No
grieve	No	No	Yes	No

keen (noun)	grieve (noun)
a funeral lament sung with loud wailing

keen (adjective)	grieve (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

keen (verb)	grieve (verb)
express grief verbally	feel grief
	cause to feel sorrow