mortarboard
US /ˈmɔːrtərbɔːrd/
UK /ˈmɔːrtərbɔːrd/

1.
an academic cap with a flat square top and a tassel, traditionally worn by students and faculty at graduation ceremonies
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Graduates proudly wore their caps and gowns, with the mortarboard perfectly balanced on their heads.
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The tradition of wearing a mortarboard dates back to the 14th and 15th centuries.
2.
a board with a handle, used by masons for holding and carrying mortar
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The bricklayer spread the mortar onto the bricks using his trowel and a fresh supply from the mortarboard.
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He carried the mortarboard filled with cement mix to the construction site.