Everyone recognises the word. Far fewer people know that it is one of the oldest living scraps of Latin in daily European speech, or that it travelled to Sicily by a route almost nobody expects. Here is where Don comes from, and what it has meant to the people who carried it.
It begins with the Latin for lord
The root is dominus, the Latin word for lord, master, owner of the house. In late and medieval Latin it wore down in speech to domnus, and then to a single blunt syllable: don. The feminine ran the same course. Domina, the lady of the house, became donna. That second word travelled so far into ordinary speech that it is now simply the Italian word for woman, which is a quiet piece of history in itself: every time an Italian says donna, they are saying mistress of the house. The same root gave us madonna, literally my lady, and the monastic and Portuguese Dom, the one that survives on a bottle of Dom Pérignon.
How the word reached Sicily
Sicilians did not inherit Don straight from Rome. It came back to the island later, and it came from Spain. After the rising of the Sicilian Vespers in 1282 the crown of Sicily passed to Aragon, and for the four centuries that followed the island was governed in the Spanish manner, latterly by viceroys sent from a distant court. Spanish court style came with them, and in Spain don and doña were already the fixed mark of a gentleman and a lady. The usage settled deepest in the south of Italy, in Sicily, Naples and Calabria, which is exactly where Spanish rule sat longest. It never took hold in the north in the same way. If you want to know why a Sicilian grandfather is Don and a Milanese one is not, that is the reason.
Who was allowed to say it
At first, very few. In medieval Spain the honorific was reserved for royalty and the highest nobility, and using it without the standing to match was a serious presumption. Over the sixteenth and seventeenth centuries it loosened, first to the lesser nobility, then to anyone of visible consequence: the man with the land, the man with the education, the man the town deferred to. By the time the Bourbons ruled Naples and Sicily, Don had become less a rank than a recognition. It was granted by the people around you rather than issued from above, and once a town had decided you were Don, you were.
It goes before the first name, never the surname
This is the rule most outsiders get wrong, and the one detail that marks out someone who knows the custom. The honorific attaches to the given name. Don Fabrizio, Don Calogero, Donna Angelica. Never Don Corbèra. Even a prince follows it: in Il Gattopardo the Prince of Salina is addressed by everyone from his priest to his gamekeeper as Don Fabrizio, because Don is not a rank sitting above his title, it is how you speak to the man. Spain kept the same rule, which is why literature gives us Don Quixote and Don Juan and never the other way round.
Donna, and the woman of the house
Donna carried its own weight. It marked the woman who held the household and, very often, the real authority inside it: the one who ran the estate accounts, arranged the marriages and decided which quarrels were finished. In Sicilian usage it was a title of respect in the fullest sense, not a decoration borrowed from a husband. Widows in particular kept it for life.
The priest's Don
There is a second line of descent that is still going. Italian secular clergy are addressed as Don plus their first name, so the parish priest is Don Antonio to his whole village. That usage is a direct survival of the Latin dominus as a churchman's style, and it is why the most famous fictional priest in Italy is Don Camillo. In a Sicilian town you could easily meet two Dons in an afternoon, one of them ordained and one of them simply owed the courtesy.
The word Hollywood borrowed
Most people outside Italy first met the word in a film, attached to a crime boss, and it is worth being straight about that. American cinema borrowed a genuine Sicilian courtesy and gave it a menace it never had in the villages. The honorific is centuries older than the association, and in Sicily it still does its ordinary work: it is what you call an older man you respect, the way you would once have raised your hat to him. The Godfather made the word famous. It did not invent it, and it does not own it.
Why Don outlived the titles
In 1948 the new Italian Republic wrote the end of the aristocracy into law. Its Constitution declared that titles of nobility are no longer recognised, and with a line of text the princes, dukes and barons of the old order lost their standing in law. Don came through it untouched, and the reason is precise: it was never a rank. It is a form of address, a courtesy, something a community grants rather than a state confers, so there was nothing in it for a constitution to abolish. The titles went. The way Sicilians speak to one another stayed exactly as it was.
What it means on your certificate
That is the tradition our certificates draw on. A Don or Donna honorific title, inscribed to a name and sealed with the dancing Leopard, in the manner of the old Sicilian estates. It is a commemorative title, worn for the pleasure and the story of it, of the same kind the island has handed out by acclaim for four hundred years. It confers nothing in law, and it never needed to. That was rather the point of it in Sicily too.