appendix

The word 'appendix' was borrowed directly from Latin in the mid-sixteenth century.‌​‌​‍​‌​‍​‌​‍​‍​‍​‍​‍​‍​‌​‌​‍​‍​‌​‍​‍​‍​‌​‍​‍​‌​‌​‌​‌​‍​‍​‍​‌​‍ The Latin 'appendix' (genitive 'appendicis') meant 'an addition,' 'an attachment,' or 'something hung on,' from the verb 'appendere' (to hang upon, to attach), composed of 'ad-' (to, upon) and 'pendere' (to hang, to weigh). The PIE root behind 'pendere' is *spend- (to pull, to stretch, to spin), making the appendix, at its deepest etymology, 'the thing pulled onto' or 'hung from' a larger structure.

The Latin verb 'pendere' (to hang, to weigh) is one of the most productive Latin roots in English. 'Pendant' (something hanging). 'Pendulum' (a hanging weight that swings). 'Pending' (hanging in the balance, not yet resolved). 'Depend' (to hang from — originally to be determined by, to rely upon). 'Independent' (not hanging from anything). 'Suspend' (to hang below, to stop temporarily — something 'suspended' is 'hanging' in an incomplete state). 'Spend' (to weigh out money — in antiquity, coins were weighed rather than counted). 'Pension' (a payment — money weighed out). 'Compensate' (to weigh together, to balance one thing against another). 'Dispense' (to weigh out, to distribute). 'Ponder' (to weigh mentally). 'Pound' (a unit of weight — from Latin 'pondo,' 'by weight'). 'Preponderance' (an outweighing). All from the simple concept of hanging and weighing.

The word 'appendix' entered English first in its literary sense: a section of supplementary material added to the end of a book. The anatomical sense — referring to the vermiform appendix, the small tubular structure attached to the cecum (the beginning of the large intestine) — followed shortly after. The full anatomical name is 'appendix vermiformis' (the worm-shaped appendage), from Latin 'vermis' (worm).

The function of the human appendix has been debated since the organ was first described. Darwin regarded it as a vestigial structure — a remnant of a larger cecum that was useful in herbivorous ancestors but had lost its function in omnivorous humans. This view dominated for over a century, and the appendix became the textbook example of a vestigial organ.

However, recent research has challenged this interpretation. Studies since the 2000s suggest that the appendix may serve as a reservoir for beneficial gut bacteria, allowing the intestine to be re-inoculated after episodes of diarrheal disease that flush out the normal gut flora. The appendix is also rich in lymphoid tissue (gut-associated lymphoid tissue, or GALT), suggesting an immunological function. The discovery that the appendix has evolved independently at least 30 times in different mammalian lineages — far too many for a useless vestige — supports the idea that it provides a genuine selective advantage.

Appendectomy — surgical removal of the appendix — is one of the most common emergency surgical procedures worldwide. Appendicitis (inflammation of the appendix) occurs when the appendix becomes blocked, usually by fecal matter, and the resulting bacterial infection can lead to rupture and peritonitis (infection of the abdominal cavity), which is life-threatening without treatment. The first successful appendectomy is generally attributed to Claudius Amyand in 1735, though the procedure did not become standard until the late nineteenth century.

The plural of 'appendix' follows two patterns: 'appendices' (the Latin plural, preferred in anatomical and formal usage) and 'appendixes' (the anglicized plural, increasingly common in general usage). Both are correct.