Page "T–V distinction" Paragraph 10

In many languages, the respectful singular pronoun derives from a plural form.

Some Romance languages have familiar forms derived from the Latin singular tu and respectful forms derived from Latin plural vos, sometimes via a circuitous route.

Sometimes, singular V-form derives from a third person pronoun ; in German and some Nordic languages, it is the third person plural.

Some languages have separate T and V forms for both singular and plural ; others have the same form ; others have a T – V distinction only in the singular.