The Collaborative International Dictionary of English v.0.48:

Midst \Midst\, n. [From middest, in the middest, for older in
   middes, where -s is adverbial (orig. forming a genitive), or
   still older a midde, a midden, on midden. See Mid, and cf.
   Amidst.]
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   1. The interior or central part or place; the middle; -- used
      chiefly in the objective case after in; as, in the midst
      of the forest.
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            And when the devil had thrown him in the midst, he
            came out of him.                      --Luke iv. 35.
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            There is nothing . . . in the midst [of the play]
            which might not have been placed in the beginning.
                                                  --Dryden.
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   2. Hence, figuratively, the condition of being surrounded or
      beset; the press; the burden; as, in the midst of official
      duties; in the midst of secular affairs.
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   Note: The expressions in our midst, in their midst, etc., are
         avoided by some good writers, the forms in the midst of
         us, in the midst of them, etc., being preferred.
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   Syn: Midst, Middle.

   Usage: Midst in present usage commonly denotes a part or
          place surrounded on enveloped by or among other parts
          or objects (see Amidst); while middle is used of the
          center of length, or surface, or of a solid, etc. We
          say in the midst of a thicket; in the middle of a
          line, or the middle of a room; in the midst of
          darkness; in the middle of the night.
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The Collaborative International Dictionary of English v.0.48:

Midst \Midst\, prep.
   In the midst of; amidst. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Midst \Midst\, adv.
   In the middle. [R.] --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

midst
    n 1: the location of something surrounded by other things; "in
         the midst of the crowd" [syn: midst, thick]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "midst":
   amid, amidst, among, amongst, between, betwixt,
   betwixt and between, center, core, diameter, diaphragm, equator,
   heart, interior, kernel, mean, median, mid, middle, midmost,
   midpoint, midriff, nucleus, over, thick, thick of things,
   throughout, together with, waist, waistline, with, zone