Source : Webster's Revised Unabridged Dictionary (1913)

Indecorous \In`de*co"rous\ (?; 277), a. [L. indecorous. See
   {In-} not, and {Decorous}.]
   Not decorous; violating good manners; contrary to good
   breeding or etiquette; unbecoming; improper; out of place;
   as, indecorous conduct.

         It was useless and indecorous to attempt anything more
         by mere struggle.                        --Burke.

   Syn: Unbecoming; unseemly; unbefitting; rude; coarse;
        impolite; uncivil; ill-bred.

Source : WordNet®

indecorous
     adj 1: lacking propriety and good taste in manners and conduct;
            "indecorous behavior" [syn: {indelicate}] [ant: {decorous}]
     2: not in keeping with accepted standards of what is right or
        proper in polite society; "was buried with indecent
        haste"; "indecorous behavior"; "language unbecoming to a
        lady"; "unseemly to use profanity"; "moved to curb their
        untoward ribaldry" [syn: {indecent}, {unbecoming}, {uncomely},
         {unseemly}, {untoward}]