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.]
      [1913 Webster]

            What abridgment have you for this evening? What
            mask? What music?                     --Shak.
      [1913 Webster]

   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]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "abridgment":
   abatement, abbreviation, abstract, alleviation, aphorism, apocope,
   attenuation, bereavement, blue-penciling, bowdlerization, breviary,
   brief, cancellation, capsule, censoring, censorship, compendium,
   compression, condensation, conspectus, contraction, curtailment,
   dampening, damping, decrease, decrement, decrescence, deduction,
   deflation, deletion, depreciation, depression, deprivation,
   deprivement, digest, diminishment, diminution, disburdening,
   disburdenment, disentitlement, divestment, dying, dying off,
   editing, elision, ellipsis, epigram, epitome, erasure, expurgation,
   extenuation, fade-out, foreshortening, languishment, lessening,
   letup, lowering, miniaturization, mitigation, omission, outline,
   precis, privation, recap, recapitulation, reduction, relaxation,
   relieving, retrenchment, sagging, scaling down, shortening,
   simplicity, sketch, striking, subtraction, sum, summary, summation,
   summing-up, syllabus, syncope, synopsis, telescoping, truncation,
   weakening