I looked on Oxford's online dictionary and was able to find the names identifying orders of a given degree:

  1. primary
  2. secondary
  3. tertiary
  4. quaternary
  5. quinary
  6. senary
  7. septenary
  8. octonary
  9. nonary
  10. denary
  11. -- no term for 11th degree??
  12. duodenary

I am curious as to what would be the sequence of terms regarding a set of 'n' items? I have up to four:

  1. unary
  2. binary
  3. ternary
  4. quaternion

but I cannot seem to find anything beyond that. Does anyone know where this list may be?

  • 1
    What do you mean "set"? A "set" of two is a pair, of three a trio, of four a quartet, of five a quintet...
    – Hot Licks
    Commented May 4, 2015 at 11:57
  • @HotLicks: Not in all spheres of thought. In mathematics, a "set" is defined as a finite or infinite collection of objects in which order has no significance, and multiplicity is generally also ignored (unlike a list or multiset). (Source: Wolfram MathWorld, bit.ly/1U8iU0Q) In other words, a set is any number of things, as long as the order (and generally the number of elements) are ignored. Commented Aug 23, 2015 at 17:52
  • @HotLicks: Besides, that hardly contributes toward an answer for the question. All it does is waste time nitpicking. Commented Aug 23, 2015 at 17:53
  • Also, Will: Undenary might be a good candidate. :) As the Wikipedia page "List of Numeral Systems" (bit.ly/1U8j5t9) points out, the word for base-11 is undecimal; and as @Cerberus pointed out below, after 3 the suffixes change from -us- to -nary. So one could adapt the numeral system term for list purposes in this way. :) Commented Aug 23, 2015 at 18:01

6 Answers 6


The problem is that English uses two different kinds of adjectives to mean "first, second, etc". The ones in -ary without the -n- come from the Latin ordinals, "first, second, etc."; but they are different after 3. (An asterisk * indicates that the word is not found in (ordinary) English sources.)

  1. Primus — primary "first"
  2. Secundus — secondary "second"
  3. Tertius — tertiary
  4. Quartus — *quartary
  5. Quintus — *quintary


The -arius suffix was also used in Latin with ordinals, and secundarius means something like "second, pertaining to two, second in rank", though it often comes very close to the simple ordinal secundus. It usually adds some connotation of ranks and order in a grand system. There is also secundanus, which I believe isn't much different.

The -n- ones come from Latin distributive adjectives, "one each, two each, etc."; they were always used in plural in Latin. 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/singular/singulary "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


I believe the ones derived from ordinals were originally used to mean "second [in order]" in English, and the distributive -n- ones to mean "of two parts", or "characterised by the number 2". But then, because these meanings are related and often overlap, they got mixed up, resulting in the current defective lists, where the -n- forms serve both senses from 4 up.

The number one is the strangest exception of all, where a new word unary was made up, though no Latin equivalent exists (there is only unus, "one", but that is like using *duary from duo, "two"). Nonary is odd as well.

These are the Latin cardinal numbers for reference:

  1. Unus/una/unum/etc. (depending on gender and case) — "one"
  2. Duo/duorum/duarum/etc. (depending on case and gender) — "two"
  3. Tres/trium/etc. (depending on case)
  4. Quattuor
  5. Quinque
  6. Sex
  7. Septem
  8. Octo
  9. Novem
  10. Decem
  11. Undecim
  12. Duodecim
  13. Tredecim


  • 2
    ah, that's why I couldn't find a separate listing ... that's fine then for my purposes; the terms were going to be used in naming functions/classes in a library I am developing, and I was trying to be as grammatically accurate as I could. That's not usually a big deal for us programmers, but I tend to be more finicky about certain things than others.
    – Will
    Commented May 13, 2011 at 12:51
  • 2
    @Will: An excellent attitude! Users of the future with literary tastes will appreciate it in your software! Commented May 13, 2011 at 12:56
  • The word trinary does exist: “Most multiple star systems are triple stars, also called trinary or ternary.”
    – tchrist
    Commented Jul 23, 2013 at 22:51
  • while coming up for short names for number systems and possible name-sharing, could we call base 0, "imaginary" ? (and i don't mean in the math sense, back off trig calculus!) Commented Sep 5, 2014 at 15:26
  • @osirisgothra: Hah, I think Trig calculus would poison your food and seduce your wife! But, really, what would "base 0" even mean? You can't really base a system on zero. Commented Sep 8, 2014 at 13:08

The arity of a function or operation is the number of arguments or operands that the function takes.


  • Nullary means 0-ary.

  • Unary means 1-ary.

  • Binary means 2-ary.

  • Ternary means 3-ary.

  • Quaternary means 4-ary.

  • Quinary means 5-ary.

  • Senary means 6-ary.

  • Septenary means 7-ary.

  • Octary means 8-ary.

  • Nonary means 9-ary.

Hope this helps.

  • ...and for 10... decimal.
    – Mitch
    Commented May 13, 2011 at 1:04
  • 2
    ...and alternatively base n.
    – Mitch
    Commented May 13, 2011 at 1:05
  • @Mitch No, bases are a different meaning. The words "binary" and "ternary" are used for both, but "octary" and "octal" are different.
    – aschepler
    Commented May 13, 2011 at 2:29
  • @aschepler: oops, you're right. what would the sequence be then for base n?
    – Mitch
    Commented May 13, 2011 at 2:32
  • @Mitch - 10 is Denary. See: en.wikipedia.org/wiki/Arity#Other_names .
    – Rob
    Commented Jul 10, 2017 at 18:08

I know I'm a little late here, but I thought it might be worth mentioning that Wikipedia has a great list of base systems, which goes all the way up to 16 (Hexadecimal, of course) without holes, and then on to 85 (Pentaoxagesimal). Here's a quick reproduction of part of it:

  1. unary (not actually on the main list, but listed farther down as being used in tally marks)
  2. binary
  3. ternary
  4. quarternary
  5. quinary
  6. senary
  7. septenary (used in weeks)
  8. octal
  9. nonary
  10. decimal (everybody's favorite!)
  11. undecimal
  12. duodecimal (used in hours, months)
  13. tridecimal
  14. tetradecimal 
  15. pentadecimal
  16. hexadecimal (Base16 encoding)

18 is octodecimal

20 is vigesimal

It's interesting to note that even our method of naming these systems reflects our attachment to the decimal system, as we begin to add prefixes after decimal. Also, if you want to form a higher number, it appears that you can use the following formula:

prefix for 2nd digit + prefix for 1st digit + gesimal

So, 27 is septemvigesimal. I invented this formula in answer to this question, but it appears to fit every case on the list.

Wikipedia also lists −2 as negabinary and −3 as negaternary. Theoretically, you can add the nega- prefix to anything, but I have no idea what you would use it for.


As Cerberus notes, the first list you give is a combination of two lists, both on Latin roots: ordinals for 1–3, then arities (from distributive numbers). To keep these straight, and include the corresponding words from Ancient Greek, I’ve written two Wiktionary appendices:


Here comes another late arrival at the Latin ball. First let me say that I studied Latin from the age of about eight through to 23, and in all that time I scarcely encountered the word distributive, other than in Kennedy's Latin Primer (my Latin grammar book of back then). Outside that, was the sole example: bina castra (two camps). I can explain that this is because the Latin word for the single camp, castra is plural. The singular, castrum, means a fort. The Romans saw a camp as an accretion of small 'forts' (watchtowers). So duo castra for two camps would be ambiguous. Instead, to be clear, they used this distributive number. But it is difficult to find examples of it, outside the commentaries of Julius Caesar. (I have since encountered Plautus the writer of Roman comedy as a second source.

The nearest is the Roman denarius nummus. The denarius is worth ten ases. And the first syllable is, of course, our old friend den-i - ten-(as)-sets. Otherwise, I have read quite a lot of Latin, prose and poetry, war and peace, but encountered scarcely any example. Consequently, clarity about its usage is extremely difficult.

There is a useful list of Latin numerals, including distributive numerals from the Later Latin Society: http://www.informalmusic.com/latinsoc/latnum.html. This includes a reasonable account of the meaning of distributive numbers, though the explanations leave at least me with the question "what the heck were they for?".

Such a list of numerals makes it look as if they are very widely used indeed. In fact, as far as I can tell, the binary numbers are constructed in accordance with a formative rule that allows us all the way to sets of infinity, which does not make them useful, and most can never have been used, possibly including undeni. The mathematics of bases might have given an opening, but too late, I fear!

I found a helpful explanation of distributive numbers from Allen and Greenough's Latin Grammar, cited by Dickinson College: http://dcc.dickinson.edu/grammar/latin/distributives. It provides a few other examples.

However, I have found an article in the Classical Review [Volume 21 Issue 7 Nov 1907 by J.P.Postgate - https://english.stackexchange.com/questions/25116/what-follows-next-in-the-sequence-unary-binary-ternary], which challenges the standard name and interpretation of the so-called distributives as a misnoma. They should be called, he argues, Collectives, giving useful citations: for example, Julius Caesar's account of the Britons he encountered in which groups of ten or twelve men (deni duodenique) shared wives.


I will just add to the programming point of view that a constant, but unspecified "arity" of 2 or more, can be polyadic - and that variadic can be used if it is not constant - for example a function taking a variable number of arguments would be variadic.

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