A mortarboard is the stiff black cap with a flat square top that students and teachers wear at some universities on formal days — graduation, big ceremonies, the photograph in the gown. A tassel usually hangs from the middle of the square. In British English this is the ordinary word for that cap. In American talk people often say cap and gown and may not use mortarboard as much, though they still know it. It is a ceremony word, a little official, not something you wear to class on a Tuesday. The name is a picture: the square top looks like the flat board a builder holds, piled with mortar, the paste that sits between bricks. Though actually, in school life nobody is thinking about bricks. They are thinking of throwing the cap in the air when the degree is done.

學位帽、四方帽（畢業典禮戴的扁平方形帽）