adverb
for millennia and millennia; forever and ever
Archaic adverbial phrase expressing an extremely long time, often used in classical poetry and blessings. The phrase is fixed and not productive in modern Japanese.
「千代に八千代に」は、君が代の歌詞にも見られる古い表現だ。
"Chiyo ni yachiyo ni" is an old expression also found in the lyrics of Kimigayo.