Act and Opponency
An “Act,” in our University language, consists of a thesis and “disputation” thereon, covering continuous parts of three hours. The person “disputing” with the “keeper of the Act” is called the “opponent,” and his function is called an “opponency.” In some degrees the student is required to keep his Act, and then to be the opponent of another disputant. Much alteration in these matters has been introduced of late, with other college reforms.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894