Does today’s date ring a bell? 25 years ago today, in the settlement of the biggest antitrust case in seven decades (think Standard Oil, in 1911), AT&T—Ma Bell—agreed to divest itself of its seven so-called "baby bells." (来源：老牌的英语学习网站 http://www.EnglishCN.com)

The 1982 breakup of that powerful monopoly got us curious about monopoly and all its kin. Monopoly is the term for exclusive ownership through legal privilege, command of supply, or concerted action, and its constituents are easy to parse: mono, meaning "one," plus the Greek polein, meaning "to sell."

Monopoly contrasts with oligopoly, "a market situation in which each of a few producers affects but does not control the market." An oligopoly limited to two sellers is known as a "duopoly."

Duopoly leads us to the less-familiar duopsony, monopsony, and oligopsony. The mono-, duo- and oligo- parts of these terms are understandable; they mean "one," "two," and "few" respectively. But if the opsony part gives you pause, remember that every seller needs a buyer. The Greek ancestor opsonia meant "purchase of victuals; catering;" these three terms refer to market situations in which there are one, two, or a few buyers for a given product or service from a large number of sellers.