Apostolus
From BiblePortal Wikipedia
Apostolus [1]
is
(1) the formal missive of the judge of a lower court, whereby a cause was transferred to a higher court to which appeal had been made from him. (See Appeal).
(2.) Apostolus (or Apostolicum) Is one of the Church books in use among the Greeks, which contains the Epistles. Thus Gregory Thaumaturgus says (Serm. ii, "'De Annun. B. Virg.," p. 19), " When the gospel is read, or the Apostolicum, do not attend to the book or to the reader, by to God speaking to thee from heaven."