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 (Psa 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; Deu 27:15-26; Neh 5:13; 8:6; 1Ch 16:36). In the primitive churches it was common for the general audience to say "Amen" at the close of the prayer (1Cr 14:16).

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