[f. TWO + -NESS.] The fact or condition of being two; duality, doubleness.
1648. Hexham, II. Tweeheydt, Twonesse, or Dualitie.
1829. Jas. Mill, Hum. Mind (1869), II. 92. Abstract terms … in place of which, the words oneness, twoness, threeness, might be substituted.
1892. Sweet, N. Eng. Gram., 49. The singular expresses ‘oneness’ … The dual expresses ‘twoness.’
1908. C. Bigg, Orig. Chr., xxxii. (1909), 407. The original unity … is now perceived to be a twoness.
