Retainer Common

a fee charged in advance to retain the services of someone

"The client had to pay an annual retainer before they could officially hire the lawyer for their case."

a person working in the service of another (especially in the household)

"The butler, who had been our family's trusted retainer for thirty years, finally announced his retirement."

a dental appliance that holds teeth (or a prosthesis) in position after orthodontic treatment

"After finishing braces, she had to wear her retainer every night to keep her new smile straight."

Any thing or person that retains.

"The lawyer kept a retainer on file to ensure she would be available for any future disputes involving her clients' assets."