appendix [M16th] The appendix is a tube-shaped sac attached to the lower end of the large intestine. The word comes directly from Latin and is based on appendere ‘to hang on’, the source of other English words such as append [LME], and appendage [M17th]. Appendix is first recorded in the sense ‘section of extra matter at the end of a book or document’, the anatomy term appears early in the 17th century.