Retinue derives via Middle English from the Anglo-French verb retenir, meaning "to retain." Another word deriving from retenir is retainer, which means, among other things, "one who serves a person of high position or rank." In the 14th century, that high person of rank was usually a noble or a royal of some kind, and retinue referred to that person's collection of servants and companions. Nowadays, the word is often used with a bit of exaggeration to refer to the assistants, guards, publicists, and other people who accompany an actor or other high-profile individual in public. You might also hear such a collection called a suite or entourage, two other words derived from French.