Amen
Amen signifies divine confirmation from truth, consequently from the Lord himself because the Lord was truth itself. Therefore he so often said, "Amen I say unto you" (Matthew 5:18, 26, Revelation 3:14).
God is called the Amen, the faithful and true witness that the Lord is the truth itself. See John 14:16, 17, 19.
In Revelation 1:7, amen signifies divine confirmation. (Apocalypse Explained 40)
In Revelation 7:12, as the Lord was Truth Itself, He often said: AMEN, or VERILY, I say unto you. (Apocalypse Revealed 375, Apocalypse Explained 23)
(References: Apocalypse Revealed 23, 292)
Apocalypse Explained #40
40. Even so, Amen, signifies Divine confirmation that so it will be. This is evident from the signification of "even so," as being a confirmation of what goes before, that so it will be; and from the signification of "Amen," as being Divine confirmation (See above, n. 34).