* Barrier: This emphasizes the function of a wall as something that separates or blocks.
* Dividing line: This focuses on the wall's role in creating boundaries.
* Enclosure: This highlights the sense of containment that a wall provides.
* Protection: If the wall's purpose is to shield from danger, this noun would be suitable.
* Impasse: This signifies a wall as an obstacle or a point of no progress.
The best abstract noun will depend on the specific context you're using it in.