佛頂尊勝陀羅尼經教跡義記 2.88

2.88

唐云金剛也。解曰：三乘行位，顯教具明五種菩提，彼以聊簡。今此明者，最上菩提，萬德之源、眾行之本，性相清淨，圓滿月輪，堅若金剛，永無退轉。謂此真言加持有情，無礙神用起大悲心入一切智，名金剛菩提也。

In Chinese, it means "adamantine" (vajra). The explanation states: Regarding the stages of practice of the three vehicles, the exoteric teachings fully elucidate the five kinds of bodhi, distinguishing them briefly. What is elucidated here is supreme bodhi, the source of ten thousand virtues and the root of manifold practices, pure in nature and characteristics, a fully perfected moon disc, firm as a diamond (vajra), never retrogressing. This means that this mantra empowers sentient beings with unhindered supernatural functions, raising a mind of great compassion to enter all-knowledge, which is called adamantine bodhi.