darken vs shade

darken is not a noun while shade is a noun.

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

As verbs, shade is a hyponym of darken; that is, shade 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 off, shadow, cloud, overcast.

darken (noun)	shade (noun)
	protective covering that protects something from direct sunlight
	a representation of the effect of shadows in a picture or drawing (as by shading or darker pigment)
	a protective ornamental covering for a lamp, used to screen a light bulb from direct view
	a quality of a given color that differs slightly from another color
	a mental representation of some haunting experience
	a subtle difference in meaning or opinion or attitude
	a slight amount or degree of difference
	relative darkness caused by light rays being intercepted by an opaque body
	a position of relative inferiority

darken (verb)	shade (verb)
become dark or darker	pass from one quality such as color to another by a slight degree
make dark or darker	vary slightly
tarnish or stain	protect from light, heat, or view
	represent the effect of shade or shadow on
	cast a shadow over