from Spanish to English
In most varieties of Spanish, there are two singular forms of the second person pronoun: Usted and tú. The former is a formal pronoun, used for social superiors and new acquaintances. The latter is familiar. 'Tutear' is a verb meaning 'to address someone as "tú"'. However, the meaning isn't purely linguistic: It indicates familiarity. Thus, 'Puedes tutearme' ('You can address me as "tú"') is an invitation to familiarity. The connotation is similar to the English phrase 'to be on a first name basis with', but I can't think, off-hand, of an English term or phrase that describes personal relationships through linguistic usage in the same way.
[This also reminds me of the term 'voseo', which means 'the use of the second person singular 'vos' in place of 'tú'. 'Vos' is favoured in a few Latin American countries, including Costa Rica (the source of my familiarity with the term). This strikes me as probably different from what you're looking for.]
Bob Offer-Westort
San Francisco, California, USA
re: tutear, the same meanings, social and linguistic, apply to the French "tutoyer" and its opposite, "vousvoyer." One way French people define what makes the very rich not like you and me is that they vousvoient their children and parents.