Evolution and etymology of of usted

Usted comes ultimately from the phrase vuestra merced ("your grace"). Between the XIII and XIV centuries, the 'formal' second person singular pronoun vos had become overloaded - being used to denote many (often conflicting) social relationships, from familiar rapport, to equal formal status, to a downwards vertical status between speakers. This ambiguity necessitated the development of novel forms for 'formal' address.

In the XIV century the pronomial phrase vuestra merced (and various similar ones) emerged to fill this gap. Only vuestra merced survived, evolving over the XIV - XVI centuries into many concurrent and competing forms, before eventually settling on the modern usted:

The evolution of the form is examined in further detail in the following study:

• El desarrollo de las variantes de vuestra merced a usted, Bob de Jonge (Universidad de Groningen)

Formal pronouns before usted

Below is a diagram showing the evolution in T-V (singular, plural) pronouns in Castilian/Northern Spanish. The evolution of pronouns was slightly different in Andalusia (even today vos is still used in some very rural areas by older speakers), and very different in Latin America, as you can interpret from the changing situation below at the time the Americas were being colonised:

Detailed information on the evolution of all second person forms (from Latin through to modern Spanish) can be found in Chapter 3 of the following paper:

• Diversity and Changing Values in Address: Spanish Address Pronoun Usage in an Intercultural Immigrant Context
  _{(Chapter 3 "History and empirical studies of address pronoun use in Spanish", p.39)}, Jo-anne Hughson

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^{Note: usted is etymologically unrelated to Arabic أستاذ (ʾustāḏ).}

Ustadh means "master" in Arabic. I was not around when the word originated, nor has this been confirmed by any authority.

From Spanish Words of Arabic Origin:

Usted is interesting because the word itself is derived from the Spanish expression vuestro merced, but in fact is phonetically similar to the Arabic word for doctor/professor: “ustadh”. In Spanish, usted is a pronoun that denotes formality and is typically used when we are addressing someone in formal situations.

¿Ustedes desean algo para tomar antes de pedir la comida? _{Would you like anything to drink before ordering lunch?}

Usted is derived from "vusted", an archaic shortening of "Vuestra Merced", an old Spanish way of saying [lit.] "your mercy" (similar to the honorific "your grace").

From the Diccionario de la lengua española:

Usted
Aféreris de vusted.

The V at the beginning disappears into the syllable when said aloud, and so eventually disappeared, it seems.

Vuestra merced evolved to usted. Vuestra merced is a really antique way to say something like your highness (not literally though).