Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
a valve which opens and closes a passageway, as the cylinder port of a steam engine, by sliding back and forth across it
Used by arrangement with John Wiley & Sons, Inc.
nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A valve that slides back and forth over ports, especially one in the cylinder wall of a steam engine that permits the intake and outflow of steam to move the piston.