Ability. Not a history of doing anticompetitive behavior, just the ability to do it. Monopoly is a precondition to that abuse.
From the same page: "Obtaining a monopoly by superior products, innovation, or business acumen is legal; however, the same result achieved by exclusionary or predatory acts may raise antitrust concerns." "Finally, the monopolist may have a legitimate business justification for behaving in a way that prevents other firms from succeeding in the marketplace. For instance, the monopolist may be competing on the merits in a way that benefits consumers through greater efficiency or a unique set of products or services."
Is it a fnord? Is there some other word you would understand to mean, there's only one big-ass store people treat as the default, and if they start being dicks, we're all in deep shit?