Poetic term for a very long time, often used in classical poetry, songs, or formal well-wishing. Can imply 'forever' or 'for generations'.
I pray that this nation will flourish for a thousand years.
For a thousand years, for eight thousand years, until pebbles become boulders and moss grows upon them.
May your reign last for a thousand, nay, eight thousand generations.
永遠 is the standard modern word for 'eternity', while 千代 is a poetic, classical term evoking the same idea.
千年 literally means 'one thousand years' and is used factually, whereas 千代 is poetic and often hyperbolic, implying endless generations.
千代 also means 'a thousand years/eternity' and appears far more often in poetry and personal names than the rarer 八千代.
Standard kanji spelling; the most common written form.
Alternate kanji spelling, less common; 世 also means 'generation' or 'world'.
A native compound of 千, here read ち, and 代（よ） “age, generation,” literally “a thousand generations” and hence “eternity.”