The Collaborative International Dictionary of English v.0.48:

Decency \De"cen*cy\, n.; pl. Decencies. [L. decentia, fr.
   decens: cf. F. d['e]cence. See Decent.]
   1. The quality or state of being decent, suitable, or
      becoming, in words or behavior; propriety of form in
      social intercourse, in actions, or in discourse; proper
      formality; becoming ceremony; seemliness; hence, freedom
      from obscenity or indecorum; modesty.
      [1913 Webster]

            Observances of time, place, and of decency in
            general.                              --Burke.
      [1913 Webster]

            Immodest words admit of no defense,
            For want of decency is want of sense. --Roscommon.
      [1913 Webster]

   2. That which is proper or becoming.
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            The external decencies of worship.    --Atterbury.
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            Those thousand decencies, that daily flow
            From all her words and actions.       --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decency
    n 1: the quality of conforming to standards of propriety and
         morality [ant: indecency]
    2: the quality of being polite and respectable

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "decency":
   accommodatingness, advantage, advantageousness, advisability,
   affability, agreeableness, amiability, appropriateness,
   assured probity, becomingness, beneficialness, benevolence,
   benignity, bienseance, blamelessness, ceremoniousness, character,
   civility, cleanness, complaisance, compliance, conformity,
   convenance, convenience, convention, conventional usage,
   conventionalism, conventionality, correctitude, correctness,
   custom, decencies, decorousness, decorum, delicacy, desirability,
   dignity, elegance, erectness, estimableness, etiquette, expedience,
   expediency, fairness, feasibility, felicity, fitness, fittingness,
   form, formality, fruitfulness, generousness, genteelness,
   gentility, good character, good form, goodness, graciosity,
   graciousness, happiness, high ideals, high principles,
   high-mindedness, honesty, honor, honorableness, immaculacy,
   integrity, irreproachability, irreproachableness, justice,
   justness, kindliness, kindness, meetness, modesty,
   moral excellence, moral strength, niceness, nobility, normality,
   normativeness, obligingness, opportuneness, percentage,
   politicness, principles, probity, profit, profitability,
   properness, proprieties, propriety, prudence, pudency, pudicity,
   pureness, purity, rectitude, reputability, respectability,
   righteousness, rightness, seasonableness, seemliness, shame,
   social convention, social usage, stainlessness, suitability,
   timeliness, unimpeachability, unimpeachableness, unspottedness,
   uprightness, upstandingness, urbanity, usefulness, virtue,
   virtuousness, wisdom, worthiness, worthwhileness