2/Linguistic Note

Linguistic Note on 2|$2$
There are many words in natural language which indicate a 2|twofold collection:
 * dual, duel, brace, couple, pair, double and twin

for example.

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

This can be found in 's $1908$ translation of, in Power of Two is Even-Times Even Only, but never specifically defined there formally.