What is another word for "biplicity"?

Roget's Thesaurus (1911) lists these synonyms for "biplicity": and, biformity, binary, binate, binomial, biparous, both, brace, bracket, conduplicate, conjugate, conjugation, couple, deuce, double, doublets, dual, dualism, dualistic, duality, duet, duplex, duplicity, dyad, dyadic, gemini, mate, one, other, pair, polarity, span, tete-a-tete, the, twin, two, unijugate, unite, yoke.