(n.) An addition 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.

PS Parthian shot addendum affix afterthought allonge appendix back matter chorus coda codicil colophon commentary conclusion consequence continuance continuation double take dying words enclitic envoi epilogue follow-through follow-up infix interlineation interpolation last words marginalia note parting shot peroration postface postfix postlude prefix proclitic refrain rider scholia second thought sequel sequela sequelae sequelant sequent sequitur subscript suffix supplement swan song tag tail