## English

### Etymology

From dyad +‎ -ic. The mathematics sense was coined by American scientist Josiah Willard Gibbs in 1884 in the second half of his book Elements of Vector Analysis.

### Pronunciation

1. Pertaining to a dyad, the number two; of two parts or elements.
1. () having an arity of two (taking two arguments or operands)
• 1965 G. E. Hughes and D. G. Londey: The Elements of Formal Logic p.270
Up to now, all the expressions we have called predicates have stood for properties which it makes sense to attribute to a single individual. Such predicates are known as monadic, or one-place, predicates. There are, however, many expressions which we cannot meaningfully apply to single objects, but only to groups of two, three or more objects. We cannot e.g. sensibly say 'x is greater than', but only 'x is greater than y'. Nor can we say 'x is between', or even 'x is between y', but only 'x is between y and z'. We shall say that an expression such as 'greater than' or 'between' stands not for a property of an individual, but for a relation between individuals. Since 'greater than' stands for a relation between two individuals, we shall say that the relation in question is a dyadic or a two-place relation. Similarly, 'between' stands for a triadic or three-place relation; and we can also have four-place, five-place, etc., relations. . . . A dyadic relation holds not simply between a pair of objects, but between those objects in a certain order. It is one thing to say that Bill is father of Tom, and another thing to say that Tom is father of Bill. . . . There are, it is true, certain dyadic relations whose direction is unimportant, in the sense that whenever they hold between x and y, they also hold between y and x; 'parallel to' and 'cousin of' are examples.
2. (obsolete) binary
• 1800 Extracts from the Port-folio of a Man of Letters. The Monthly Magazine and British Register Volume X page 34
The dyadic arithmetic proposes to express all numbers by two characters, 1 and 0. The value of 1 is to double at every remove into a preceding column. Thus, 1 is represented by 1, 2 by 10, 4 by 100, and 8 by 1000; 3 is represented by 11, 5 by 101, 6 by 110, 7 by 111, 9 by 1001, and 10 by 1010. Thus far nothing seems to be gained but simplicity and there is a grievous loss of brevity. But in the huge numbers of the mathematicians this inconvenience was to fall away and the complex operations of addition, subtraction, multiplication, and division, were to sink into mere transcription.
2. Pertaining to the physical sex of a person who is exactly male or female in genetics, anatomy and hormone levels; not intersex.
Synonyms: endosex, perisex
• 2019, Katie Steele, Julie Nicholson, Radically Listening to Transgender Children, Lexington Books:
Although dyadic bodies may be more common, they are no more or less "normal" than intersex bodies.