eternal; everlasting; immortal
A yojijukugo meaning something that remains unchanged and undiminished forever. Often used in formal or literary contexts to describe principles, truths, or great works.
This work has eternal value.
His words are an everlasting truth.
永遠 is a common word for 'eternity', while 千古不磨 is a formal yojijukugo emphasizing unchanging permanence.
不朽 also means 'immortal' or 'everlasting', but 千古不磨 adds the nuance of being unpolished or undiminished over a thousand ages.
A yojijukugo composed of 千古 (a thousand ages, eternity) and 不磨 (not worn away, indestructible). The exact historical derivation is uncertain, but the phrase is conventionally associated with the idea of something that remains unchanged forever.