The Collaborative International Dictionary of English v.0.48:

Twain \Twain\ (tw[=a]n), a. & n. [OE. twein, tweien, tweyne, AS.
   tw[=e]gen, 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.
   [1913 Webster]

   In twain, in halves; into two parts; asunder.
      [1913 Webster]

            When old winter split the rocks in twain. --Dryden.
      [1913 Webster]

   Twain cloud. (Meteor.) Same as Cumulo-stratus.
      [1913 Webster]

WordNet (r) 3.0 (2006):

twain
    n 1: two items of the same kind [syn: couple, pair,
         twosome, twain, brace, span, yoke, couplet,
         distich, duo, duet, dyad, duad]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TWAIN
       Technology Without An Important Name


The Free On-line Dictionary of Computing (30 December 2018):

TWAIN

    An image capture API for Microsoft
   Windows and Apple Macintosh operating systems that
   enables the user to control a scanner or digital camera
   from image processing software.

   TWAIN was first released on 1992-02-29 and is currently
   ratified at version 2.0 as of 2005-11-28.  It is maintained by
   the TWAIN Working Group.

   Kevin Bier, chairman-emeritus of the TWAIN Working Group and
   the one of the original co-author/editors of TWAIN 1.0, chose
   the name TWAIN after reading letters by Mark Twain.  It was
   unofficially considered to mean "toolkit without an important
   name."

   The word "twain" is an archaic form meaning "two".  It appears
   in Kipling's "The Ballad of East and West" - "...and never the
   twain shall meet...", reflecting the difficulty, at the time,
   of connecting scanners and personal computers.  It was
   up-cased to TWAIN to make it more distinctive.  This led
   people to believe it was an acronym, and then to a contest to
   come up with an expansion.  None were selected, but the entry
   "Technology Without An Interesting Name" continues to haunt
   the standard.

   The TWAIN Working Group (http://twain.org/).

   (2000-02-25)


U.S. Gazetteer Places (2000):

Twain, CA -- U.S. Census Designated Place in California
   Population (2000):    87
   Housing Units (2000): 57
   Land area (2000):     7.419895 sq. miles (19.217440 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    7.419895 sq. miles (19.217440 sq. km)
   FIPS code:            80952
   Located within:       California (CA), FIPS 06
   Location:             40.018101 N, 121.048898 W
   ZIP Codes (1990):     95984
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Twain, CA
    Twain