三密之異名。其性常住堅固。故曰三金剛。密教之六大即三密也。地水火之三大為身密，空風之二大為語密，識大為意密。日本覺鍐之顯密不同頌曰：「顯理無六境，密照之三金。」 言金銀銅三者。
The three metals, gold, silver, copper. The esoterics have (a) earth, water, fire, representing the 身密 mystic body; (b) space and wind, the 語密 mystic mouth or speech; (c) 識 cognition, the 意密 mystic mind.