It was ironic that the loudest noise in the library, where silence was required, came from the librarian.

ironic 是形容词，来自名词 irony（讽刺）。这个词描述一种"与预期相反"或"具有讽刺意味"的情况，即实际发生的事情与人们期望或应该发生的事情完全相反。