N-COUNT (在英国，各大院校师生在出席正式场合时戴的)方顶帽；(在美国，学生在中学和大学毕业典礼时戴的)学位帽 A mortar board is a stiff black cap which has a flat square top with a bunch of threads attached to it. In Britain, mortar boards are sometimes worn on formal occasions by university students and teachers. In the United States, mortar boards are worn by students at graduation ceremonies at high schools, colleges, and universities. (在英国，各大院校师生在出席正式场合时戴的)方顶帽；(在美国，学生在中学和大学毕业典礼时戴的)学位帽