(n.) An appendix or addition; as, an addendum to a report\.

PS Parthian shot accession accessory accident accidental accompaniment addenda additament addition additive additory additum adjunct adjuvant afterthought annex annexation appanage appendage appendant appendix appurtenance appurtenant attachment augment augmentation auxiliary back matter chorus coda codicil collateral colophon complement conclusion concomitant consequence contingency contingent continuance continuation corollary double take dying words envoi epilogue extension extra extrapolation fixture follow-through follow-up happenstance incidental increase increment inessential last words mere chance nonessential not-self offshoot other parting shot pendant peroration postface postfix postlude postscript refrain reinforcement rider second thought secondary sequel sequela sequelae sequelant sequent sequitur side effect side issue subscript subsidiary suffix superaddition supplement swan song tag tailpiece undergirding unessential