Who came up with the names for "day" and "night"?
Day comes from the Old English word daeg, meaning both day and lifetime, and may go as far back as the Sanskrit word dah, meaning burn (like the sun).Night is from the Old English niht, then the Proto-Germanic nakht.
Definitely not me.
Sammy is right. See Genesis 3:1-5
God. When hey mad the world in seven days. He said let there be light and there was and he named it day. Same with night.