2/Linguistic Note

Linguistic Note on $2$ (two)

There are many words in natural language which indicate a twofold collection:

dual, duel, brace, couple, pair, double and twin

for example.

Words derived from or associated with the number $2$ include:

bicycle: a vehicle with $2$ wheels

An archaic term for an instance of the number two is dyad.

This can be found in Sir Thomas L. Heath's $1908$ translation of Euclid: The Thirteen Books of The Elements, in Power of Two is Even-Times Even Only, but never specifically defined there formally.

In the words of Euclid:

Each of the numbers which are continually doubled beginning from a dyad is even-times even only.

(The Elements: Book $\text{IX}$: Proposition $32$)

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $2$
• 1996: John H. Conway and Richard K. Guy: The Book of Numbers ... (previous) ... (next): Chapter $1$: The Romance of Numbers: Number Words
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $2$