postscript vs letter

postscript and letter both are nouns.

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

postscript (noun)	letter (noun)
a note appended to a letter after the signature	a written message addressed to a person or organization
textual matter that is added onto a publication; usually at the end	the conventional characters of the alphabet used to represent speech
	an award earned by participation in a school sport
	a strictly literal interpretation (as distinct from the intention)
	owner who lets another person use something (housing usually) for hire

postscript (verb)	letter (verb)
	mark letters on or mark with letters
	set down or print with letters
	win an athletic letter