Oretta appears to be the Italian form of Arete, a Greek name meaning “Virtue.” The best-known form of the name is of course Aretha. Oretta appears in the first story of the sixth day of The Decameron. While travelling with some friends, a knight offers to help her out by telling her a story to make the time pass quicker. However, he tells it so badly, she begs him to stop. He’s much better at taking a hint than telling a story, so he amiably agrees to talk about other things for the remainder of their journey.
Osbech is probably a variant of the name Usbek, whose true etymology is in much question. However, its ultimate origins seem to be Turkic. Osbech appears in the seventh story of the second day, as at least the eighth man to take the passive Alatiel as a lover. (I know I shouldn’t hold Medieval beliefs to the same standards as modern realities, but I’m far from the only person who’s a bit uncomfortable with how The Decameron, for all its empowered women, still depicts intercourse as the be-all and end-all of a woman’s sexual delight. That’s not how most women reach ecstasy, particularly not until they’ve been doing it for awhile!)
Anyway, Osbech is King of the Turks and frequently at war with the Emperor of Constantinople. While he’s in Smyrna, he goes to attack the Emperor’s son Constanzio, whom he’s heard is on the island of Chios, living a lascivious life with some woman he’s stolen and taking no measures to protect himself. Osbech and his men destroy the city and kill or take prisoner many of Constanzio’s men, and Osbech of course discovers the beautiful Alatiel, whom he marries.
Several months later, Osbech goes to war against the King of Cappadocia, an ally of the Emperor of Constantinople. Osbech is killed and his army defeated, and his vassal Antioco proceeds to seduce Alatiel.