Appendix:English arities and adicities

English has two series of arities, functioning as distributive numbers: one from Latin (arities), one from Ancient Greek (adicities). The Latinate series is commonly used, particularly binary, while the Ancient Greek one is much less common.

The Latinate series is frequently confused with ordinal numbers, as both end in -ary. This is most significant for quaternary (arity, used for both) vs. quartary (ordinal) and novenary (arity) vs. nonary (ordinal, used for both). The Latinate series is also used for names of the lower positional numeral systems (binary, ternary), but not from base-8 (octal, not *octonary) upwards.

For polynomials, both these numbering systems are used at once. For example, a degree two polynomial in two variables, such as $x^{2}+xy+y^{2}$, is called a “binary quadratic”: binary due to two variables, quadratic due to degree two. See English polynomial degrees for a full list.

number	Latinate	Grecian
0	nullary	niladic, medadic
1	unary	monadic
2	binary	dyadic
3	ternary	triadic
4	quaternary	tetradic
5	quinary	pentadic
6	senary	hexadic
7	septenary	heptadic
8	octonary	octadic
9	novenary	enneadic
10	denary	decadic
11	undenary	endecadic
12	duodenary	dodecadic
20	vigenary	icosadic

See also

• Appendix:English ordinal numbers
• Appendix:English polynomial degrees