Someone wrote about his mortar-board in the Japanese notebook section. I thought he was talking about the surface of the wall, but it was about a hat which the university students wore at the graduation. I was surprised!
How come does this word have totally different two meanings? Did European carpenters wear such square hats a long time ago?
Why I misunderstood is that he wrote モルタルボードin Japanese. It is exactly a kind of walls!