Seemly vs Decorous - What's the difference?

Seemly is a related term of decorous.

is that seemly is (of behavior) appropriate; suited to the occasion or purpose; becoming while decorous is marked by proper behavior.

is appropriately, fittingly.

(er)

(of behavior) Appropriate; suited to the occasion or purpose; becoming.

His behavior was seemly , as befits a gentleman.

* Shakespeare

I am a woman, lacking wit / To make a seemly answer to such persons.

* Hooker

Suspense of judgment and exercise of charity were safer and seemlier for Christian men than the hot pursuit of these controversies.

* apposite

* unseemly

* * * seemliness

(en adverb)

Appropriately, fittingly.

* 1590 , Edmund Spenser, The Faerie Queene , II.i:

The great earthes wombe they open to the sky, / And with sad Cypresse seemely it embraue [...].

(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.