Lewis & Short

āmēn [[??]; Gr. ἀμήν] (eccl. Lat.).

  1. I. Adj., true, faithful: (tu Deus) fecisti mirabilia, cogitationes fideles, amen (Heb. [??] = verity), Vulg. Isa. 25, 1.
  2. II. Subst., truth, faith fulness: qui benedictus est, benedicetur in Deo amen, in the God of faithfulness, Vulg. Isa. 65, 16: haec dicit Amen (Gr. ὁ Αμήν), He that is True, ib. Apoc. 3, 14.
  3. III. Most freq. adv.
    1. A. Prop., to confirm words spoken by one’s self or another, So be it; Fr. Ainsi soit-il; LXX. γένοιτο, Amen: et respondebit omnis populus, Amen, Vulg. Deut. 27, 15; 5, 22 et saep.: Gratia vobiscum, Amen, ib. 2 Tim. 4, 21: cui (Deo) honor et gloria in saecula saeculorum, Amen, ib. Rom. 16, 27 et saep.
    2. B. In gen., truly, surely, verily; very freq. in the phrase. Amen dico vobis, Vulg. Matt. 5, 18 al.; ib. Marc. 3, 28 al.; ib. Luc. 4, 24 al.; and in St. John: Amen, amen dico vobis, ib. Joan. 1, 51 al. (The a is long in Aus. Eph. ap. Orat. fin., and Prud. Cath. 4, 72, but short in Paul. Nol. Poëm. 17 ad Nicet. 117.)