Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
a piece forming or attached to the side of something
Used by arrangement with John Wiley & Sons, Inc.
The 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 part forming the side of something else: a chair with curved sidepieces.