notation vs postscript

notation and postscript both are nouns.

Word	Noun	Adjective	Verb	Adverb
notation	Yes	No	No	No
postscript	Yes	No	No	No

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

notation (noun)	postscript (noun)
the activity of representing something by a special system of marks or characters	a note appended to a letter after the signature
a technical system of symbols used to represent special things	textual matter that is added onto a publication; usually at the end
a comment or instruction (usually added)