Where does “ок” come from?

ок (Russian) comes from Russian оке́й, from English okay, from English ok — Alternative letter-case form of OK.

Ancestry of “ок”, step by step

StepLanguageWordMeaning
1Russianоке́йOK, okay
2EnglishokayAlternative spelling of OK
3EnglishokAlternative letter-case form of OK
Every word from English ok →Every word from English okay →Every word from Russian оке́й →