This is the 5984th most frequent Polish word.
ścianę
"Ścianę" means "a wall" (accusative case).
Here, 'ścianę' (the accusative case of 'ściana', meaning 'wall') is used as the object of the verb to show the action performed onto the wall.
Powiesiłem obraz na ścianę.
I hung a picture on the wall.
In this context, 'ścianę' is the direct object that receives the action of repainting, described by the verb.
Odmalowaliśmy ścianę w jadalni.
We repainted the wall in the dining room.
The noun 'ścianę' is used in the accusative case to denote the surface being leaned against, indicated by the preposition 'o' (against).