mortarboard，英语单词，主要用作名词，作名词时译为“学位帽；灰泥板”。

柯林斯英汉双解大词典

mortarboard ( mortarboards )

1.N-COUNT A mortarboard is a stiff, black cap which has a flat, square top with a bunch of threads attached to it. In the United States, mortarboards are worn by students at graduation ceremonies at high schools, colleges, and universities. 学位帽

mortarboard ĥ 灰板