I was curious to know what comes after:

Primary, secondary, tertiary, ...

This Oxford website says it is "quartenary, quinary, ..."

But they are already taken!

Unary, binary, ternary, quaternary, quinary, ...

And according to this EL&U post deriving from the Latin originals should give:

Primary, secondary, tertiary, quartary, quintary, ...

Wiktionary says that "quartary" (from the ordinal) is correct, but "quaternary" (from the distributive number) is common especially in biology.

So, what should it really be in English?

  • I've never heard of quartary or quintary, only quaternary which is about as high as I would expect people to know. After that, we just use the English ordinals, 5th, 6th &c.
    – JDF
    Jan 24, 2018 at 12:30
  • @Deonyi: The words "first, second, third" do not mean the same as "primary, secondary, tertiary". We can say "the primary reason for X is Y" to mean "the most important/significant reason for X is Y", whereas "first" will not be suitable for this.
    – user21820
    Jan 24, 2018 at 14:46
  • Yes, but after quaternary their meanings blur. This happens even lower, however you have to use a construction like 'the first and foremost'.
    – JDF
    Jan 25, 2018 at 5:21
  • @Deonyi: Well the fact that you use "foremost" shows that "first" does not work there. And there is no similar construction for "secondary".
    – user21820
    Jan 25, 2018 at 8:36
  • Just found this interesting article and thought I'd include it here. There are words like duodenary and vigenary. english-for-students.com/Primary-1.html Jul 26, 2023 at 8:36

4 Answers 4


Logically it should be "quartary" because the Latin is "third" = "tertius"; "fourth" = "quartus"

In the first, we deleted the "us," hence "quartary."

I can see a 1773 publication in the search results for "quartary" that uses the word: https://books.google.com/books?id=1-UEAAAAQAAJ

  • Thanks a lot for sharing your finding! The first page uses both "tertiary" and "quartary" in the same sentence, with the meaning I am looking for.
    – user21820
    Feb 23, 2018 at 8:45
  • @user21820 It hasn't been 1731 for quite some time now. Quartary, quintary, etc. are obsolete. As per Deonyi's comment to OP, current usage is "quaternary" (or even just "fourth"), then the regular English ordinals.
    – Spencer
    Feb 23, 2018 at 10:18
  • 2
    Extremely rare. Quaternary is the common term instead.
    – Kris
    Feb 23, 2018 at 10:51

Here is something I was able to discover on the internet the prime time I confronted the same predicament as you.

  • 1st = primary
  • 2nd = secondary
  • 3rd = tertiary
  • 4th = quaternary
  • 5th = quinary
  • 6th = senary
  • 7th = septenary
  • 8th = octonary
  • 9th = nonary
  • 10th = denary
  • 12th = duodenary
  • 20th = vigenary.

These come from the Latin roots. The -n- ones come as well from Latin but this time are distributive adjectives, "one each, two each, etc."; they are always used in plural. They were sometimes also used in a sense roughly similar to the ordinals, which is probably why English uses them in an odd way.

  1. (Singuli — single "one each")
  2. Bini — binary "two each"
  3. Terni/trini — ternary/*trinary
  4. Quaterni — quaternary
  5. Quini — quinary
  6. Seni — senary
  7. Septeni — septenary
  8. Octoni — octonary
  9. Noveni — *novenary
  10. Deni — denary
  11. Undeni — *undenary
  12. Duodeni — duodenary
  13. Terni/trini deni — *ternidenary/*tridenary
  • 1
    Does the second list come from the EL&U post I cited in my question? If so, you should state your source.
    – user21820
    Feb 14, 2018 at 11:39

I think this was an etymological error by the French geologist Jules Desnoyer in Annales des sciences naturelles in 1829. He considered the five periods described by Charles Lyell, then proposed new names for just four periods (now roughly the Jurassic, Cretaceous, Paleogene+Neogene, and Quaternary). Shortly thereafter, he reconsidered the Quaternary and declined to put real support behind it. He wrote in French and called the period the "Quaternaires." This had some influence, though apparently not a lot immediately. But being a textbook, it surely influenced later French geologists.

For instance, Frenchman Émile Haug used the term in the third fascicule of vol. 2 of his textbook Traité de Geologie published in 1911. I know I'm skipping ahead 82 years, but this is hard to research, OK? Haug divided post-Cretaceous time (i.e. the Cenozoic Era) into three periods and renamed them and adjusted boundaries. Apart from the upsetting decision to name the last of three periods "fourth" (for continuity with Desnoyer), he preserved the etymological mistake conflating "quartus" with "quaternius." And somehow from this origin we are stuck with the bizarre nomenclature to this day. I think this use of "quaternary" where "quartary" makes more etymological sense spread from geology to other disciplines like biochemistry decades later. By now, "quartary," to the extent that it was ever really a word at all, has essentially disappeared. It was always so rare a word that a single significant application (an anglicized Fench geologic period) swamped all prior uses, and only "quaternary" survived.

In 1911, a Frenchman writing only as J.W.G. submitted a review of Haug's work to nature. He wrote it in English of course, and in several parts. At one point he brings up this very incongruity. I can't find Haug's text, but in the review, J.W.G. states,

"The post-neogene deposits Prof. Haug groups together as the Quaternary, the term proposed by Desnoyers in 1829. He rejects Lyell's term Pleistocene on the grounds that it is not euphonious, and 'tout à fait', incorrect. But is Quaternary any better in these respects? Quaternarius means 'consisting of four,' 'containing four,' as it is defined, for example, in Lewis and Short's 'Latin Dictionary.' The term is properly employed in quaternion and in quaternary compounds, but not for the name of a fourth division of geological time. Should it not be Quartary?"

Etymologically-speaking, he is correct. "Quartary" would have made more sense as a coinage. Later that year, in the same journal Nature, A. Irving Bishop of Strattford made a brief response titled A Point in Geological Nomenclature. I find it difficult to evaluate in terms of sincerity. He assures J.W.G. that an etymologically correct "das Quartar" was used in the German textbook Elemente der Geologie by Hermann Credner of Leipzig in 1908. This may have been a typo, as in fact the German name for the period is "das Quartär," and Bishop does not forget the umlaut in "das Tertiär."

At any rate, there have been complaints over this strange word for well over a century, and likely longer, but by now it is here to stay. Blame Desnoyer, I guess, and maybe Haug for ensuring that confused term would stick. The other posters are right that "quartary," while more logical, practically does not exist at all, except occasionally in explanations about what went wrong with the word "quaternary." Evidently, as late as the 18th century, it saw very occasional use, but this never approached the eventual significance of the geological term "Quarternary Period." For what it's worth, the association with "fourth" is a far more confusing feature in geology than the etymological confusion between distributives and ordinals. In what sense is the Quaternary Period the "fourth" anything? In no sense, that's what.

  • Wow you must have spent a long time writing this up. Thanks! By the way, you can register for an account if you want to keep this answer associated to you. =)
    – user21820
    Jun 2, 2023 at 17:34

In a science context, the next term would be Quaternary Structure.

http://www.particlesciences.com/news/technical-briefs/2009/protein-structure.html is where is got this from.

I am not sure about what comes after this.

  • Yeap I'm aware of the use of "quaternary structure" in biology, as stated in my question. =)
    – user21820
    Feb 14, 2018 at 11:37

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