immutable law; indestructible canon
Poetic set phrase referring to an unchangeable fundamental law or canon, especially the Meiji Constitution. Rare in modern everyday language; mainly encountered in historical or literary contexts.
See also: 大日本帝国憲法
The Constitution of the Empire of Japan was regarded as an immutable law.
The specific constitution often referred to as 不磨の大典; the phrase itself is a poetic epithet for it.
From 不磨 (imperishable, indestructible) + の + 大典 (great code/law). The exact historical origin is uncertain, but it became a set phrase associated with the Meiji Constitution.