1. To exercise authoritative or dominating influence over; direct. See synonyms at conduct.
2. To adjust to a requirement; regulate: controlled trading on the stock market; controls the flow of water.
3. To hold in restraint; check: struggled to control my temper.
4. To reduce or prevent the spread of: control insects; controlled the fire by dousing it with water.
5. 1. To verify or regulate (a scientific experiment) by conducting a parallel experiment or by comparing with another standard.
   2. To verify (an account, for example) by using a duplicate register for comparison.

1. Authority or ability to manage or direct: lost control of the skidding car; the leaders in control of the country.
2. 1. One that controls; a controlling agent, device, or organization.
   2. An instrument or set of instruments used to operate, regulate, or guide a machine or vehicle. Often used in the plural.
3. A restraining device, measure, or limit; a curb: a control on prices; price controls.
4. 1. A standard of comparison for checking or verifying the results of an experiment.
   2. An individual or group used as a standard of comparison in a control experiment.
5. An intelligence agent who supervises or instructs another agent.
6. A spirit presumed to speak or act through a medium.

[Middle English controllen, from Anglo-Norman contreroller, from Medieval Latin contrārotulāre, to check by duplicate register, from contrārotulus, duplicate register : Latin contrā-, contra- + Latin rotulus, roll, diminutive of rota, wheel.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.