Monism and meaning

Monism must refer to something that actually exists. What is it?

Matter. Material monism is by definition referring to matter.

I am not sure what the confusion is here.

Every instance of Meaning must have something “that means”.

How is meaning related to ontology? Monism is a about what exists, not what something means. Semantics is the domain for this.

As I have said before, we ask what exists (ontology), how do we know (epistemology) and what is its meaning (semiotics). Together then we ask what is the meaning (semantics).