The square academic cap, graduate cap, cap, mortarboard (because of its similarity in appearance to the mortarboard used by brickmasons to hold mortar) or Oxford cap ...
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is an item of academic dress consisting of a horizontal square board fixed upon a skull-cap, with a tassel attached to the centre. In the UK and the US, it is commonly referred to informally in conjunction with an academic gown as a "cap and gown". It is also sometimes termed a square,: 17 trencher,: 17 : 915 or corner-cap. The adjective academical is also used.