Decorous, a.
Etymology: [L. dec, 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.
Shades of meaning
Fernald has no entry of its own for decorous; he lists it under becoming.
Where he writes about it:
The dignity and gravity of a patriarch would not be becoming to a child; at a funeral lively, cheery sociability would not be decorous, while noisy hilarity would not be decent; sumptuous display would not be suitable for a poor person. — from becoming