In the theory of Topological Vector Spaces, there are several examples of function spaces and their duals. For example, $\mathcal{D}(\Omega)$ (the smooth function with compact support in $\Omega$) and $\mathcal{D}'(\Omega)$ (Distributions in $\Omega$), $\mathcal{S}(\mathbb{R}^n)$ (Schwartz space).
My question: I would like to know if there is any reason or what was the reason for denoting by $\mathcal{E}'(\Omega)$ the space of distributions with compact support in $\Omega$. That is, why use the letter $\mathcal{E}$?
Generally the notation has some relation with the name of the space or with some property of it. But in this case, I can't see that.