unchecked = uncontrolled, unregulated Often companies which monopolise certain market sectors are regulated the government.

To "check" can mean "to hold back." To "hold something in check" is to restrain it and slow it down. In the United States monopolies are generally illegal. There are exceptions. It would be crazy to have three private water companies digging up the streets, each running pipes to some houses but not others. Such situations are called "natural monopolies." They are allowed, but they are regulated. In towns with a private water company, there's only one company. If it raises its prices, you have to pay--you can't take your business to another water company. However, they aren't free to set their prices to anything they'd like. They can't just "charge what the traffic will bear." Their prices need to be approved by the state public utilities commission. The commission reviews the company's business and allows them to make a fair profit, but no more. It is not an unchecked monopoly. The monopoly power of the water company is held in check by the public utilities commission.

Monopoly - exclusive control of a commodity or service in a particular market, or a control that makes possible the manipulation of prices. OR an exclusive privilege to carry on a business, traffic, or service, granted by a government. Unchecked -- not prevented from continuing or growing. So an unchecked monopoly is a free to grow, no objection business/ service allowed by government. For example, government of North Korea is unchecked monopoly. This is because there is single political party which controls everything which is offered by any government.