The Collaborative International Dictionary of English v.0.48:

Abridgment \A*bridg"ment\ (-br[i^]j"ment), n. [OE. abregement.
   See Abridge.]
   1. The act of abridging, or the state of being abridged;
      diminution; lessening; reduction or deprivation; as, an
      abridgment of pleasures or of expenses.
      [1913 Webster]

   2. An epitome or compend, as of a book; a shortened or
      abridged form, esp. of a written work; an abbreviation.
      [1913 Webster]

            Ancient coins as abridgments of history. --Addison.
      [1913 Webster]

   3. That which abridges or cuts short; hence, an entertainment
      that makes the time pass quickly. [Obs.]
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            What abridgment have you for this evening? What
            mask? What music?                     --Shak.
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   4. a diminution or curtailment, as of legal rights.
      [PJC]

   Syn: Abridgment, Compendium, Epitome, Abstract,
        Synopsis.

   Usage: An abridgment is made by omitting the less important
          parts of some larger work; as, an abridgment of a
          dictionary. A compendium is a brief exhibition of a
          subject, or science, for common use; as, a compendium
          of American literature. An epitome corresponds to a
          compendium, and gives briefly the most material points
          of a subject; as, an epitome of history. An abstract
          is a brief statement of a thing in its main points. A
          synopsis is a bird's-eye view of a subject, or work,
          in its several parts.
          [1913 Webster]

WordNet (r) 3.0 (2006):

abridgment
    n 1: a shortened version of a written work [syn: condensation,
         abridgement, abridgment, capsule]