a tool with two blades that are at a fixed angle to one another, used to bevel a mitre joint
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Examples from the Web for mitre square
Historical Examples of mitre square
When permanently fixed at an angle of 45, it is called a mitre-square.
By placing this bevel against the edge a try-square of this construction can also be used as a mitre-square (Fig. 682).