noun (n)

• a note appended to a letter after the signature(noun.communication)

  Synonym:
  ps
  

  source: wordnet30
• textual matter that is added onto a publication; usually at the end(noun.communication)

  Synonym:
  addendum, supplement
  

  source: wordnet30
• A paragraph added to a letter after it is concluded and signed by the writer; an addition made to a book or composition after the main body of the work has been finished, containing something omitted, or something new occurring to the writer.(noun)

  source: webster1913