Cornelius J. Moynihan & Sheldon F. Kurtz, Introduction to the Law of Real Property 10 n.2 (4th ed. 2005):

Originally the most honorable form of tenure, tenure by knight service gave to the tenant in the twelfth century not only land ownership but also avoice in the great council and jurisdiction over his subtenants.(2)

(fn2) Attendance in the king’s court by tenants-in-chief and at the lord’s court by under-tenants was an auxiliary service attaching to most tenures. In medieval times the word “court” was not restricted to a tribunal presided over by a professionally trained judge sitting with or without a jury. As to suit at court, see 1 Pollock & Maitland 586-594.