Regular language? Union of the dictionary and an non-regular language I'm attempting to figure out if a union of two languages is regular.

$$
L_1 = \{all\ the\ words\ in\ the\ Oxford\ dictionary\} \\
L_2 = \{w : w\ has\ twice\ as\ many\ a's\ as\ b's\}
$$

$L_2$ is well established to be a non-regular language. However, I am not sure if $L_1$ would be considered a regular language. The language should be finite (albeit large), which suggests it is regular, but I'm not certain.

If $L_1$ is regular, then I would consider the union $L_1 \cup L_2 $ would also be regular, as by the same argument, the language would be finite.

What does everyone think?
The best way to see that $L_1 \cup L_2$ is not regular is through closure properties of the regular languages.

Theorem. If $L_1$ is finite and $L_2$ is not regular, then $L_1 \cup L_2$ is not regular.

Proof. Since $L_1 \setminus L_2$ is finite, it is regular.
Suppose $L = L_1 \cup L_2$ were regular. Then $L \setminus (L_1 \setminus L_2) = L_2$ would also be regular, contrary to assumption. $\qquad\square$