marking vs shading

marking and shading both are nouns.

Word	Noun	Adjective	Verb	Adverb
marking	Yes	No	No	No
shading	Yes	No	No	No

As nouns, shading is a hyponym of marking; that is, shading is a word with a more specific, narrower meaning than marking:

marking: a pattern of marks
shading: graded markings that indicate light or shaded areas in a drawing or painting

Other hyponyms of marking include blaze, crisscross, cross, mark, eyespot, ocellus, dapple, fleck, maculation, patch, speckle, spot, bar, streak, stripe.

marking (noun)	shading (noun)
evaluation of performance by assigning a grade or score	a gradation involving small or imperceptible differences between grades
the act of making a visible mark on a surface	graded markings that indicate light or shaded areas in a drawing or painting
a pattern of marks
a distinguishing symbol