also: まんごう
noun
eternity; an extremely long time
Buddhist term for an immeasurably long period, often used in phrases like 万劫末代 (for all eternity). Rare in everyday speech; mainly literary or religious.
万劫末代まで語り継がれるであろう。
It will be passed down for all eternity.
この苦しみが万劫も続くのかと思うと絶望的になる。
I feel despair when I think this suffering might continue for an eternity.
永遠 is the common word for 'eternity' in modern Japanese. 万劫 is a much rarer, more literary Buddhist term.
From Buddhist terminology, combining 万 (ten thousand, myriad) and 劫 (kalpa, an extremely long period in Buddhist cosmology). The exact historical derivation is uncertain, but it is used to express an immeasurably long time.