noun, adverb
A somewhat literary or formal word for an endless span of time. Often used in set phrases like 万古不易 (eternally unchanging) or 万古長青 (evergreen). As an adverb, it can mean 'forever' or 'for all eternity'.
この真理は万古不易である。
This truth is eternally unchanging.
彼の名は万古に輝くだろう。
His name will shine for all eternity.