Source : Webster's Revised Unabridged Dictionary (1913)

Decorous \De*co"rous\ (?; 277), a. [L. dec[=o]rus, fr. decor
   comeliness, beauty; akin to decere. See {Decent}, and cf.
   {Decorum}.]
   Suitable to a character, or to the time, place, and occasion;
   marked with decorum; becoming; proper; seemly; befitting; as,
   a decorous speech; decorous behavior; a decorous dress for a
   judge.

         A decorous pretext the war.              --Motley.
   -- {De*co"rous*ly}, adv. -- {De*co"rous*ness}, n.

Source : WordNet®

decorously
     adv : in a proper and decorous manner; "he pretended to be pleased
           and applauded decorously" [ant: {indecorously}]