"Medius" is Latin for "middle" or "in the middle".
Here are some other words with the root "medius":
* Median: the middle value in a set of numbers
* Medieval: relating to the Middle Ages
* Meditate: to think deeply and quietly
* Mediator: a person who helps resolve a conflict
* Mediocre: of average quality
* Medium: the means by which something is communicated or expressed