To exercise authoritative or dominating influence over; direct. See Synonyms at conduct. To adjust to a requirement; regulate: controlled trading on the stock market; controls the flow of water. To hold in restraint; check: struggled to control my temper. To reduce or prevent the spread of: control insects; controlled the fire by dousing it with water. To verify or regulate (a scientific experiment) by conducting a parallel experiment or by comparing with another standard. To verify (an account, for example) by using a duplicate register for comparison. Authority or ability to manage or direct: lost control of the skidding car; the leaders in control of the country. One that controls; a controlling agent, device, or organization. An instrument or set of instruments used to operate, regulate, or guide a machine or vehicle. Often used in the plural. A restraining device, measure, or limit; a curb: a control on prices; price controls. A standard of comparison for checking or verifying the results of an experiment. An individual or group used as a standard of comparison in a control experiment. An intelligence agent who supervises or instructs another agent. A spirit presumed to speak or act through a medium.