GNU Collaborative International Dictionary of English

Found one definition

1.       
   Twain , a. & n. [OE. twein, tweien, tweyne, AS. twēgen, masc. See Two.] Two; -- nearly obsolete in common discourse, but used in poetry and burlesque. “Children twain.”
   Chaucer.
   
   1913 Webster
   And whosoever shall compel thee to go a mile, go with him twain.
   Matt. v. 41.
   
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   In twain, in halves; into two parts; asunder.
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   When old winter split the rocks in twain.
   Dryden.
   
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   -- Twain cloud. (Meteor.) Same as Cumulo-stratus.
   1913 Webster