Today, the word myriad refers to an extremely large number, with no specific amount implied. However, historically it meant "ten thousand", just like million means "1,000,000". That noun comes from French myriade, which is from Latin myrias, with the same definition. That's from Ancient Greek myrios, which was a bit more abstract. It could mean "infinite", "countless", or "boundless", basically serving the same function as gazillion or bajillion do in informal English today. Finally, myrios is of uncertain origin, but the prevailing theory is that it derives from the Proto-Indo-European reconstruction meue, which roughly translates to "push away" and is also the source of words like motility, motive, motif, promote, remote, and many others. Usage of myriad has been increasing in literature over time since its introduction in the mid-sixteenth century.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.