他的笔记太潦草了，完全无法辨认。

His notes were so messy that they were completely illegible.

illegible 是由前缀 il-（表示否定）和形容词 legible（清晰可读的）组成的形容词。legible 来自拉丁词根 legere（阅读），所以 illegible 的字面意思是"无法阅读的"，即"难以辨认的、字迹模糊的"。