Decorous vs Mannerly - What's the difference?

As adjectives the difference between decorous and mannerly

is that decorous is marked by proper behavior while mannerly is polite, having good manners.

(en adjective)

Marked by proper behavior. (rfex)

* 1919 ,

But who can fathom the subtleties of the human heart? Certainly not those who expect from it only decorous sentiments and normal emotions.

(en adjective)

polite, having good manners

* 1593, William Shakespeare, Two Gentlemen of Verona

Lucetta, as thou lov'st me, let me have / What thou think'st meet, and is most mannerly .

* 1861, Charlotte Yonge, The Young Step-Mother

...but Genevieve's laugh roused her again, partly because she thought it less mannerly than accorded with the girl's usual politeness.

* mannerliness