No, they are actually synonyms.
They mean about the same thing. A+
The noun countenance means a face or a look or appearance. There are no direct antonyms for the noun, as close as you can come are faceless, expressionless, or featureless. The verb countenance is to accept, approve or support something; antonyms for the verb are deny, disagree, disapprove, discourage, dispute, reject, oppose, renounce, or repudiate.
The countenance refers to a person's facial expression, while demeanor refers to their outward behavior or conduct. The relationship between the two is that one's countenance can often reflect their demeanor, as facial expressions can convey emotions or attitudes that align with one's behavior.
The word "demeanour" is pronounced as dih-MEEN-er.
Her countenance was glowing!
Countenance is the appearance of a calm facial expression. A sample sentence using the word countenance is, Jane's face looked countenance when the dog jumped out in front of her.
face or visage for one meaning of countenance tolerate or accept for another meaning of countenance
His countenance turned from pleasant to angry at the words spoken by his boss. In this example countenance refers to facial expression. The company does not countenance corporate espionage. This example means to approve of or tolerate something, in this case corporate espionage.
It is a noun!
The countenance refers to the face. Countenances means to approve or at least not object.
The more he was depressed the more his countenance fell.
I have no idea what the word countenance means. Is that good enough?