tutoyer

In conversational French, the pronoun "vous" ("you") is used for formal address of individuals (as well as plural addressees familiar or otherwise), while the singular pronoun "tu" (also "you," a relative of Middle English "thou") is reserved for use among intimate friends. A person who uses "tu" to address his or her elders, for example, is committing a breach of etiquette. The French verb tutoyer - literally, "to address with the pronoun 'tu'" - was borrowed into English in the late 17th century to refer to this concept. In many cases, the English verb is still used in reference to people speaking French (as English does not discriminate between intimate and formal address in its pronouns), but it is occasionally used to describe casual address among close English speakers.