noun /əˈpɛn.dɪks/
a) Specifically, a text added to the end of a book or an article, containing information that is important to but is not the main idea of the main text
idleness is an appendix to nobility; they count it a disgrace to work, and spend all their days in sports, recreations, and pastimes [...].
b) The vermiform appendix, an inner organ without known use that can become inflamed.
Wikipedia foundation.