D defs.my
Entry 1 sense Webster, 1913

Addendum

/əd-ĕn'-dəm/ · Ad·den·dum · IPA /əˈdɛn.dəm/
01 n. A thing to be added; an appendix or addition.
pl. Addenda
  1. 1.
    A thing to be added; an appendix or addition.
Phrases & compounds
Addendum circle — the circle which may be described around a circular spur wheel or gear wheel, touching the crests or tips of the teeth.