Definition of "twain"

Since I haue your good leaue to goe away,I will make haſt; but till I come againe,No bed ſhall ere be guilty of my ſtay,Nor reſt be interpoſer twixt vs twaine.

c. 1596–1598 (date written), William Shakespeare, “The Merchant of Venice”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene ii], page 176

A month or twain to live on honeycombIs pleasant;

1866, Algernon Swinburne, Before Parting, lines 1–2

Oh, East is East and West is West, and never the twain shall meet.

1889, Rudyard Kipling, The Ballad of East and West, line 1

And whenever Sir Chetwynd spoke of his "young girls" he was moved to irreverent smiling, as he knew the youngest of the twain was at least thirty.

1897, Marie Corelli, “Chapter I”, in Ziska: The Problem of a Wicked Soul, New York: Stone & Kimball, page 25

[…] all too soon we twain shall treadThe bitter pastures of the dead:Estranged, sad spectres of the night.

1900, Ernest Dowson, Amor Profanus, lines 26–28

The susceptible twain, on the search for adventure, dropped in.

1903 February 8, The Truth, Sydney, page 3, column 3