Media was an ancient empire which directly preceded the Persian Empire. This area of northeastern Iran existed along the collective trails which would later be known as the silk road. Media, as we now know and pronounce this word, was “madiya” or “madhya,” inherited from Proto-Indo-European (PIE) into their pre-Iranian languages such as Avestan, Old Persion, Sanskrit, and which means “middle.” To name an empire based on its middle-ness (spatially, I presume) privileges the recognition of its central status, say, perhaps in mediating commerce along the silk road between China and the Mediterranean. (Which is a conjecture on my part.)
The concept of “middle” came into Latin, also by inheritance from PIE, as “medius.” Its related Latin forms are mediatorum (one who mediates), mediatus (to mediate), mediocris (middle quality), and so on. English gets a lot of its Latin roots through French, so going from “medius” to “medium” or “intermediate” is not a difficult stretch. As reported in the OED the phrase “intermediate agency” meant “channel of communication,” first recorded in 1605. A nineteenth century “medium” could be one who communicates with the dead, or a splotch of oil paint on canvas, both arguably a channel of communication.
The phrase “mass media” was born about 1923 when used as a technical term in advertising, and applied to newspapers by about 1927. By the 1960s, media in all its forms as “channel of communication” was further abstracted by media theorist Marshal McLuhan to mean “any technological extension of ourselves.”
Looking up “media” and “medium” in the OED will deluge you with a number of definitions perhaps exceeding 60. How’s this one: “the middle layer of the wall of a blood vessel or lymphatic vessel,” or this one: “a voiced stop in ancient Greek”?
The common thread running through all of these seemingly wide and varied set of definitions is the concept of “intermediation between two things,” a form of being in the middle. When the intermediation occurs between a human being and something else, we come back to a channel of communication, or a tool, or as McLuhan said, an extension of ourselves.