miter box

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A fixed or adjustable device for guiding handsaws in cutting miter joints or in making crosscuts, especially an open-ended box with slotted sides.

from The Century Dictionary.

• noun In carpentry, a long narrow wooden box consisting of a bottom and two sides in which kerfs at an angle of 45 (or some other angle) are cut for the reception of a saw: used in cutting pieces of wood to form miter-joints.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun hand tool for guiding handsaws in making crosscuts or miter joints