Addendum

Etymology
From the gerundive of addere:.

Noun

 * 1) Something to be added; especially text added as an appendix or supplement to a document.
 * 2) A postscript.
 * 3)  The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line.

Thesaurus
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