Amen

This Hebrew word means firm, and hence also faithful (Rev.
3:14). In Isa. 65:16, the Authorized Version has "the God of
truth," which in Hebrew is "the God of Amen." It is frequently
used by our Saviour to give emphasis to his words, where it is
translated "verily." Sometimes, only, however, in John's Gospel,
it is repeated, "Verily, verily." It is used as an epithet of
the Lord Jesus Christ (Rev. 3:14).

It is found singly and sometimes doubly at the end of prayers
(Ps. 41:13; 72:19; 89:52), to confirm the words and invoke the
fulfilment of them. It is used in token of being bound by an
oath (Num. 5:22; Deut. 27:15-26; Neh. 5:13; 8:6; 1 Chr. 16:36).
In the primitive churches it was common for the general audience
to say "Amen" at the close of the prayer (1 Cor. 14:16).

The promises of God are Amen; i.e., they are all true and sure
(2 Cor. 1:20).