retainer

noun

1. Any thing or person that retains.
2. A dependent or follower of someone of rank.

   “If they possessed the means to marshal labour, pile up food resources and provender armies of year-round retainers, what sort of royalty would consciously elect not to do so.”

3. A paid servant, especially one who has been employed for many years.

   “Of all this family lore I knew but little and vaguely; only what is to be gathered from the fireside talk of old retainers in the nursery.”

4. A fee one pays to reserve the other's time for services.

   “This lawyer charges a retainer for his work.”

5. A device that holds teeth in position after orthodontic treatment.

   “You give me head / It makes it worse / Take out your fuckin' retainer / Put it in your purse”

6. A retaining valve.