How to say "once, at some time" in Russian?

Когда-то

"once, at some time" is Когда-то in Russian.

Когда-то means "once, at some time" in English.

Listen to the pronunciation

Word #336 of 4,000 by frequency in Russian — level A1.

Example

Когда-то мы были лучшими друзьями в школе.

We were once best friends at school.