The term is used in two senses. It is applied first to a book or document whose contents are invested with a special authority, in virtue of which the work is called authentic. In its second sense it is used as a synonym for "genuine", and therefore means that a work really emanates from the author to whom it is ascribed. The article VULGATE explains the first sense of the word; the articles on the single books of Sacred Scripture illustrate the second.
The Catholic Encyclopedia, Volume II. Published 1907. New York: Robert Appleton Company. Nihil Obstat, 1907. Remy Lafort, S.T.D., Censor. Imprimatur. +John M. Farley, Archbishop of New York