"exvius" is a latim neologism they created for the game that has the same roots as latim words such as "obvius" (obvious) or "devius" (devious). In this case, "vius" is a form of the latim word "via", which means "path". "Ex" is a bit more complicated since it can have a few different meanings in latim, the most common of which is "from", but it can also have a few other nuances (including "old", "completely" or "outside") when used in conjunction with some words.

"exvius" in our case means something like "outside of the path"