I recently found out that French has two different words for "you."
Tu is the familiar "you," which demonstrates a certain closeness and informality. ... Vous is the formal "you." It is used to show respect or maintain a certain distance or formality with someone. ... Vous is also the plural "you" - you have to use it when talking to more than one person, no matter how close you are.
French is from the Romance language family, as far as I know.
I was immediately reminded of the verse (Malachi 1:6):
וְאִם-אָב אָנִי אַיֵּה כְבוֹדִי וְאִם-אֲדוֹנִים אָנִי אַיֵּה מוֹרָאִי
This (from Hebrew) literally means: "But if I [G-d] am a father, where is My honor? And if I am masters, where is My fear?" The word "masters" is in the plural, but it uses the word "I" and "My" in the singular! (As a side note, Hebrew has a different word for "you" s. and "you" pl.)
It is interesting to note that the major biblical commentators — among them Rashi, who ordinarily deals with simple questions in the text, such as translations; and Radak and Ibn Ezra, who were both grammarians — don't address this. The first one to address this was the Metzudos who writes (in Metzudas Tziyon): "It is the practice of the scripture to mention the name of 'mastery' in plural language; similarly, 'The masters of Joseph' (Gen. 39:20)."
Is there any relation between this French grammar rule and the Hebrew rule, in which the plural is also used for respect? (If there is, it would solve the problem of why Rashi didn't say anything about it, since he was French.) Is there any known reason how this Semitic language can end up with something that a Romance language has?