I have always thought the word annulus to be exceptionally awkward. I'd like to know the relation between annulus and anus.

Geometrically, an annulus is a disk with a hole in it. The anal muscle ("sphincter") has an annular shape.

I'm wondering how we got from annulus to anus.

4 Answers 4


You have the derivation slightly backwards. The Latin anus meant ring and thus also the anatomical anus.

Meanwhile anulus was a Latin diminutive of anus, so a small ring


Both anus and annulus comes from Latin, where anus meant "a ring," and annulus meant "a little ring." The Latin annulus is derived from the Latin word anus.

The origin of anus is 16th century, and the origin of annulus is Middle English.

  • 1
    Can it be that one of our most fantasized- and obsessed-over orifices was not named until the 16th century? Just my quick reaction, but how can this make sense? Mar 25, 2011 at 18:28
  • 4
    @Pete: Wikipedia (en.wikipedia.org/wiki/Changes_to_Old_English_vocabulary) lists the following obsolete English words for it: earsgang, setl, and ūtgang.
    – Alex
    Mar 25, 2011 at 21:09
  • @Alex - Fascinating, thanks! We can see that ūtgang is something like out-going; and the Wikipedia article relates the ears- of earsgang to arse. Apr 24, 2011 at 8:57

Online Etymology Dictionary has it "from PIE base *ano- 'ring.'" Interesting.


Annulus is also related to annual, or the yearly cycle. Related to Anno Domini - Year of Our Lord. The double 'n' seems to be correct historically although they have a common origin.

Not necessarily surprising that anus may not have been named until the 16th C. The hip bone ("innominate") is the "unnamed" bone. The pudendal nerve (the one that goes numb if you've been riding a bike for too long) means "that which is not to be discussed" and is also related to the slang "pud".

  • Roy Film: It seems entirely plausible that "annulus" and "annual" share a common root. But can you provide a citation confirming that? Sep 23, 2021 at 4:34

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