法華義疏 1.213

1.213

「阿若憍陳如」者，此名有本有末，憍陳如者此云火器，是其本姓，從姓以立名也。阿若者，後得道時加此名也。阿之言無，若之言智，以悟無而生智故名阿若；蓋是道俗雙舉，名姓合題。

Regarding "Ājñātakauṇḍinya": this name has a root and a branch. "Kauṇḍinya" is translated here as "fire vessel"; it is his original clan name, and his name was established according to the clan. "Ājñāta" was this name added later when he attained the Way. *Ā* means non-existence, and *jñāta* means wisdom; because he awakened to non-existence and generated wisdom, he was named Ājñāta. This is a case of presenting both the sacred and the secular, combining the name and the clan name.