Source : Webster's Revised Unabridged Dictionary (1913)

Indecorum \In`de*co"rum\, n. [Pref. in- not + decorum: cf. L.
   indecorous unbecoming.]
   1. Want of decorum; impropriety of behavior; that in behavior
      or manners which violates the established rules of
      civility, custom, or etiquette; indecorousness.

   2. An indecorous or becoming action. --Young.

   Syn: Indecorum is sometimes synonymous with indecency; but
        indecency, more frequently than indecorum, is applied to
        words or actions which refer to what nature and
        propriety require to be concealed or suppressed.
        Indecency is the stronger word; indecorum refers to any
        transgression of etiquette or civility, especially in
        public.

Source : WordNet®

indecorum
     n 1: a lack of decorum [syn: {indecorousness}] [ant: {decorum}, {decorum}]
     2: an act of undue intimacy [syn: {familiarity}, {impropriety},
         {liberty}]