mortarboard

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

• noun A square board with a handle used for holding and carrying masonry mortar.
• noun An academic cap topped by a flat square.

from The Century Dictionary.

• noun A board, generally square, used by masons to hold mortar for plastering.
• noun A square-crowned academic cap.

from the GNU version of the Collaborative International Dictionary of English.

• noun A small square board with a handle beneath, for holding mortar; a hawk; used by masons to hold or carry mortar.
• noun An academic cap topped by broad, projecting, stiff and flat square top, with a tassel attached to the top and hanging down. It was once worn by students in some colleges, but is now worn usually only at graduation ceremonies.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A square board, with a handle, on which mortar or plaster is carried: a hawk.
• noun An academic cap that has a flat square top with a tassel.

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

• noun a square board with a handle underneath; used by masons to hold or carry mortar
• noun an academic cap with a flat square with a tassel on top