[kawa]

"Thou" sounds very similar to german "du" which is the current informal form. In older german the second person plural ('Ihr', similar to "vous" french from which "you" may come) was also the formal form, but it's out of fashion for a few centuries now.

[LAC-Tech]

Indeed, it's the same word! In the ancestor language of both English and German (and also Dutch, Low German, and many others) it's been reconstructed as "þū".

[amelius]

What is the ancestor language, and how do you pronounce þū?

[pvg]

proto-West Germanic by current thinking (at least, by Wikipedia)

https://en.wikipedia.org/wiki/West_Germanic_languages#Validi...