medius

Medius, media, medium declines like bonus, and the thing to learn is not the endings but the syntax. It is a partitive adjective: media urbs does not mean "the middle city" but "the middle of the city", and Latin puts as an adjective what English wants as a noun plus "of". Summus mons is the top of the mountain, extremus liber the end of the book, ima valles the bottom of the valley. Once you see the pattern it is everywhere.

Second sense: standing between, hence "intervening" of time and "neutral" or "meddling" of a person. Medius is also a noun in the neuter, in medio, "in the middle, in public view". Family: medium, medietas, mediator, meridies (from medi-dies, "midday"), mediocris. English medium, mediocre, mediate, immediate, medieval and Mediterranean, the sea in the middle of the land; Spanish medio, French moyen and mi-.