Thanks! I’ll add “polite you” and/or “formal you”, as an alternative meaning to make things more clear.
I think in this case, there is a degree of semantic drift at play. Though “thou” was once considered more informal, due to the fact it is now associated with more archaic English, which is usually read in more formal settings (e.g., quoting of KJV Bible, Shakespeare) it is now considered more formal. Sort of like how in the article linked “terrific” once meant “inducing terror” and now means “wonderful”.