retainer

plural retainers

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.

   2021 October 19, David Graeber, David Wengrowr, “Unfreezing the ice age: the truth about humanity’s deep past”, in The Guardian, UK

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.

   1865, Sheridan Le Fanu, Uncle Silas

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

   This lawyer charges a retainer for his work.

5. dentistryA 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

   1981, “Too Drunk to Fuck”, performed by Dead Kennedys

   1 more example

   I've known you since the third grade. I've hand-washed your retainer. I keep mint-flavored Oreos at the house for you.

   2017, Mike Oppenhuizen, Jen Regan, “The D-Train to Bone Town” (27:47 from the start), in Michael Patrick Jann, director, Atypical, season 1, episode 6, spoken by Elsa (Jennifer Jason Leigh), via Netflix

6. engineeringA retaining valve.