* Density: This is the most direct and common abstract noun for "dense," referring to the degree of compactness or concentration.
* Thickness: This is a more specific abstract noun, focusing on the physical dimension of density.
* Concentration: This refers to the amount of something contained within a specific space.
* Complexity: This refers to the intricacy or difficulty of something, often used metaphorically for dense information or ideas.
The best choice will depend on the specific situation you are trying to describe.