milestone vs marking

milestone and marking both are nouns.

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

As nouns, marking is a hypernym of milestone; that is, marking is a word with a broader meaning than milestone:

Other hypernyms of milestone include mark, marker.

milestone (noun)	marking (noun)
stone post at side of a road to show distances	evaluation of performance by assigning a grade or score
a significant event in your life (or in a project)	the act of making a visible mark on a surface
	a pattern of marks
	a distinguishing symbol