postscript vs annotation

postscript and annotation both are nouns.

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

As nouns, annotation is a hypernym of postscript; that is, annotation is a word with a broader meaning than postscript:

Other hypernyms of postscript include notation, note.

postscript (noun)	annotation (noun)
a note appended to a letter after the signature	the act of adding notes
textual matter that is added onto a publication; usually at the end	a comment or instruction (usually added)