A person who owns one or more shares of stock in a jointstock company or a corporation. Synonymous with stockholder. Shelley's Case, rule in See rule in Shelley's Case. n. Sherman Antitrust Act The definitive antitrust statute, passed by Congress in 1890, that prohibits monopolies or unreasonable combinations of companies to restrict or in any way control interstate commerce. Specifically outlawed is two or more persons engaging in monopolistic practices, such as price fixing, although it doe...