Definition of "atwain"

[S]uch ſmiling rogues as theſe, / Like Rats oft bite the holy cords a twaine, / Which are t' intrince, t' vnlooſe: […]

c. 1603–1606, William Shakespeare, “The Tragedie of King Lear”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act II, scene ii], page 292, column 1

Clear-headed friend, whose joyful scorn, / Edged with sharp laughter, cuts atwain / The knots that tangle human creeds, / The wounding cords that bind and strain / The heart until it bleeds, […]

1842, Alfred Tennyson, “To—”, in Poems. […], volume I, London: Edward Moxon, […], page 15

[…] a much wider valley into which a great reef of rocks thrust out from the high mountain, so that the northern half of the said vale was nigh cleft atwain by it;

1896, William Morris, chapter 11, in The Well at the World’s End‎, volume 2, London: Longmans, Green, page 55

You must believe me that on this street, neither in the houses which line it, nor the cobblestones which pave it, nor the elevated structure which cuts it atwain, neither in any creature that bears a name and lives thereon, neither in any animal, bird or insect passing through it to slaughter or already slaughtered, is there hope of “lubet,” “sublimate” or “abominate.”

1939, Henry Miller, Tropic of Capricorn, Grove Press, published 1962, page 295