add.

/AE1 D/
noun
  1. 1

    Something to be added; especially text added as an appendix or supplement to a document.

  2. 2

    A postscript.

  3. 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.

Source: https://en.wiktionary.org/wiki/add., https://en.wiktionary.org/wiki/addendum