Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
an instrument consisting of two pieces set at right angles, used for testing the accuracy of square work and for marking off right angles
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 carpenter's tool consisting of a ruled metal straightedge set at right angles to a straight piece, used for measuring and marking square work.