marking vs milestone

marking and milestone both are nouns.

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

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

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