What is Advocatus?

Legal Definition
An advocatus, or advocate, was generally a medieval term meaning "lawyer". The term was also used in continental Europe as the title of the lay lord charged with the protection and representation in secular matters of an abbey, known more fully as an advocatus ecclesiae.
-- Wikipedia
Legal Definition
In the civil law. An advocate; one who managed or assisted in managing another's cause before a judicial tribunal. Called also "patrons." Co.d. 2, 7, 14. But distinguished from casidicus. Id. 2, 0, 6.
See also
-- Black's Law Dictionary
Legal Definition
A pleader, a narrator. Bract. 412 a, 372 b.
-- Bouviers Law Dictionary