Why doesn't an extra-terrestrial always stay at home on Earth?
Why are extramural studies not written up on the walls?
Honestly, no wonder everyone's confused.
Word To Use Carefully Today: extra. This word has only been around in English since the 1700s. It may have started off as a shortened form of extraordinary, in which case it comes from the Latin extrā, beyond, from exterus, outside.
This means we're in the silly situation where extra- can mean even more, as in the word extravagant (from extra plus vāgarī, to wander) or even less, like extraordinary (outside the ordinary) or literally outside (as in extramural, outside the walls of a teaching institution).
By the way, an extra- (or more usually extro-) vert is someone who focuses naturally on the external world rather than on his or her inner life.
Vertere is Latin for to turn.