darken vs shadow

darken is not a noun while shadow is a noun.

Word	Noun	Adjective	Verb	Adverb
darken	No	No	Yes	No
shadow	Yes	No	Yes	No

As verbs, shadow is a hyponym of darken; that is, shadow is a word with a more specific, narrower meaning than darken:

Other hyponyms of darken include embrown, murk, dun, blind, dim, dim, bedim, benight, shade, shade off, cloud, overcast.

darken (noun)	shadow (noun)
	refuge from danger or observation
	something existing in perception only
	an indication that something has been present
	a premonition of something adverse
	an unilluminated area
	a spy employed to follow someone and report their movements
	an inseparable companion
	a dominating and pervasive presence
	shade within clear boundaries

darken (verb)	shadow (verb)
become dark or darker	follow, usually without the person's knowledge
make dark or darker	make appear small by comparison
tarnish or stain	cast a shadow over