Before we start, a quick distinction: something is only a monopoly if it single-handedly controls an entire industry. If it shares that power with a few other countries, as many corporations do today, it's an oligopoly, where the influence is held by and the terms are dictated by a few rich companies. All right, into the etymology: the word monopoly came to us in the early sixteenth century from the Romans, whose word monopolium came from the Greeks. Here we can separate the word into its components: monos, meaning "single", and polein, meaning "to sell". This alludes to how a monopoly is a specific person or business is the single one to have selling rights for a particular product. Monos comes from the Proto-Indo-European root men, meaning "isolated", polein comes from the PIE root pel, also meaning "to sell", and that's the whole story.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.