In feudal times, a retainer may be an individual who serves, is contracted, or is indebted to a lord, king or emperor. These individuals ranged from knights and lords in Europe, to warlords and samurai in Asia. Similar to a vassal.
Between shareholders, a judge may be asked to replace an executive who holds shares with a retainer if they believe there is a danger of the executive running the company into the ground
Retainer agreement, a contract between two people or companies where one pays to reserve the other's time. The agreement includes the salary to be paid, the period of time to be reserved (for instance, one week per month), and details on the type and scope of work to be done by person or company under retainer