nonsuch

She is nonsuch in her field.→She is a nonsuch in her field.

nonsuch 是名词，表示“无与伦比的人或物”，用作表语时前面需要加冠词 a，直接说“is nonsuch”缺少冠词，语法错误。

There is nonsuch person here.→There is no such person here.

nonsuch 是名词，意为“典范、极品”，不能表示“没有这样的”。学习者误将 nonsuch 等同于 no such，混淆了词义和用法。