marking vs postmark

marking and postmark both are nouns.

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

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

marking: a distinguishing symbol
postmark: a cancellation mark stamped on mail by postal officials; indicates the post office and date of mailing

marking (noun)	postmark (noun)
evaluation of performance by assigning a grade or score	a cancellation mark stamped on mail by postal officials; indicates the post office and date of mailing
the act of making a visible mark on a surface
a pattern of marks
a distinguishing symbol

marking (verb)	postmark (verb)
	stamp with a postmark to indicate date and time of mailing