A retinue is a group of people that accompany an important person. If you're a king or queen, you can think of a retinue as your royal crew or posse.
Retinue shares a root with retain. This fact can help you remember the word. If you hire someone to help you out while you travel, you are retaining their services. When their services are retained, they become part of your retinue. The Secret Service could be thought of as the U.S. President's retinue. Another example: A celebrity's retinue might include a hair dresser, a personal assistant, and a toy poodle.