Don, from Latin dominus, is a Spanish (pron. d̪on), Portuguese (Domdõ), and Italian honorific title, and largely as the cultural translation of "Sir". It is, however, no order of chivalry. It is usually used as a mark of high esteem for a distinguished Christian hidalgo or fidalgo; that is, a nobleman
The honorific was also used among Ladino-speaking Sephardi Jews, as part of the Spanish culture which they took with them after the Expulsion of the Jews from Spain in 1492. Its abbreviation, particularly in Portuguese, is "D." It is still used in reference to priests, like the French Dom. The treatment was reserved for those who had royal or some higher old noble ancestry, as well as some title bearers who had their title without needing but the King's confirmation instead of authorization, the so called titles de Juro e Herdade. In Brazil it was not used in reference to nobles, but was used to refer to royals (both to the monarch and to princes), and, in the ranks of the clergy, it is only used to refer to Bishops or other senior ecclesiastical hierachs.
The use is roughly comparable to the style The Honourable of British custom, but closer to Lord or Lady, although the analogy is a loose one, at best. The female version is Doña (Spanish, pron. IPA: ['d̪o.ɲa]) and Dona (Portuguese, pron. IPA: ['do.nɐ]) abbreviated "Dª" or simply "D.".
The traditional usage of the honorific is Don for the Royals, Grandees of Spain and his relatives, and don as a courtesy respectful treatment for everyone else of some position. In Portugal, the feminine form has been used as a compliment for elderly women irrespectively of birth and rank, but is often seen as an ageing treatment.
Don/Dom or Doña/Dona is attached to a person's given name. It is generally preceded by the acronym Sr. (for Señor): 'Sr. Don Diego de la Vega,' 'Don Diego de la Vega,' or simply 'Don Diego' (the secret identity of Zorro). Attachment to the surname without the given name, for example 'Don de la Vega,' is incorrect.
Nowadays it is often used as a standard form of address in Spain, similarly as Mister is in English. In Spain the title is sometimes used to refer to a graduate of High School.
In the Philippines, Don/Dom or Doña/Dona is used to refer to wealthy influential people as a substitute to the more common "Señor" or "Señora".
The title spread to the Kingdom of Naples and Sicily during the Spanish domination of southern Italy in the 16th Century. Officially, it was the style to address a noble (as distinct from a reigning) prince (principe) or duke (duca), and their children and agnatic descendants. The feminine is "Donna". Genealogical databases and dynastic works still reserve the title for this class of noble by tradition, although it is no longer a right under Italian law. Informally, especially in the countryside, any Italian nobleman might be addressed or referred to as Don. For example King Carlos III of Spain was widely known in his Neapolitan realm as "Don Carlo". Sometimes it would be preceded by further honorifics like "L'Illustrissimo" (The illustrious) or "Il Magnifico" (The magnificent) depending on the official rank or style of the honoree.
As in Spanish usage, Don is prefixed either to the full name or to the person's given name, never to the surname alone. One would be called "Don Francesco Gonzaga" or just "Don Francesco", but never "Don Gonzaga". As a further example a titled nobleman may be styled "Il Signor Marchese Don Lelio Carafa" [The Lord Marquess Sir Lelio Carafa]. An untitled nobleman or wealthy property owner would have been styled "Il Signor Don Francesco Gonzaga" [The Lord Sir Francesco Gonzaga]. A priest would be addressed as Don + Name + position such as "Don Marco Di Lorenzo, Arciprete" [Don Marco Di Lorenzo, Archpriest] or for a bishop "Monsignore Don Francesco Pignatelli, Vescovo di Benevento" [Monsignor (title for an Italian bishop) Don Francesco Pignatelli, Bishop of Benevento". Casually a priest would be called "Don Marco" whereas a Bishop would be called "Monsignore".
Today in Italy, the title is more rarely used and only used for Catholic priests and titled noblemen. Some priests today prefer the title "Sac." or Sacerdote (literally "priest").
At Oxford and Cambridge universities, members of the academic staff are sometimes referred to as a Don - a remnant of the time when these universities were considered religious institutions and their staff a kind of clergy. In practice within Oxford it is used to refer to fellows of the colleges. At Cambridge it is rarely, if ever, used.
Dona Beija, a Brazilian TV series.