The Collaborative International Dictionary of English v.0.48:

Amen \A`men"\ (?; 277), interj., adv., & n. [L. amen, Gr.
   'amh`n, Heb. [=a]m[=e]n certainly, truly.]
   An expression used at the end of prayers, and meaning, So be
   it. At the end of a creed, it is a solemn asseveration of
   belief. When it introduces a declaration, it is equivalent to
   truly, verily.

   Note: It is used as a noun, to denote:
   (a) concurrence in belief, or in a statement; assent;
   (b) the final word or act;
   (c) Christ as being one who is true and faithful.
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             And let all the people say, Amen.    --Ps. cvi. 48.
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             Amen, amen, I say to thee, except a man be born
             again, he can not see the kingdom of God. --John
                                                  ii. 3. Rhemish
                                                  Trans.
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   To say amen to, to approve warmly; to concur in heartily or
      emphatically; to ratify; as, I say Amen to all.
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