Furthermore, we cannot confidently deduce the meaning of a word in the later development of a language even if we clearly establish the original meaning of that word. Thus, the meaning of the word derived from the root 'mn can hardly be explained by determining its original meaning. And when we do not know the original meaning, the development of a word can lead us far from that meaning to something entirely different. The meaning of a word cannot be inferred from the (more or less certain) etymology, but only by a careful study of the way it is used in the language. [Alfred Jepsen, "'mn," Theological Dictionary of the Old Testament, vol. 1, Revised Edition, G. Johannes Botterweck and Helmer Ringgren, eds., translated by John T. Willis (Grand Rapids: Eerdmans, 1974), page 293.]
There are two other uses of 'amen which are different in their use from the above 27 instances, but where 'amen can similarly be transliterated, "A/amen," namely, in Isaiah 65:16 (discussed in 5., below). Jepsen ("'mn," pages 320-322) notes the following five (5) Hebrew Bible uses of 'amen according to these texts:
These last uses in Isaiah 65:16 bring us into the New Testament use of the same expression, though it is only used once in this way (Revelation 3:14). Apart from this one instance where it appears to parallel the use of the same word in the Hebrew text of Isaiah 65:16 (compare also the way the "Amen" speaks in Revelation 3:2, 12, again paralleling the "God of Amen" language found in Isaiah 65), the majority of NT uses of amen have Jesus as the most frequent user.
However, unlike the common use of "amen" today to conclude speech or prayers, Jesus uses "Amen, amen" (doubled for emphasis) twenty-five (25) times to begin his speech. Never does Jesus use "amen" or even "amen, amen" to conclude a prayer or a blessing, not even when concluding his model prayer for others to use.—See Matthew 6:9-13; Luke11:1-4.
Of course, there is nothing in the books of the Bible which is made 'invalid' (Matthew 15:6; Mark 7:13) by a tradition which uses "amen" in a discreet or in an expressed, appropriate manner to show a person's acceptance of what has already been said, or to otherwise give an affirmative response or assurance when concluding our own prayers, or at the end of any prayer said for and accepted by others.
This is something which early Christians did do according to 1 Corinthians 14:16, and possibly also according to 2 Corinthians 1:20, though this latter example may involve saying "amen" at times other than at the end of written or spoken prayers or expressions.—See also Romans 1:25; 9:5; 11:36; 15:33; Galatians 1:5; 6:18.
On the other hand, there is no reason why this one word ('amen) must always be used to give forth such expression, or as a part of a prayer to God or at the end of a blessing said for a group or family. So next time you conclude your prayer, try ending it with an expression of meaning which you personally can accept as similar to "amen," such as, "May these things be so." It may make your calls and prayers to God more personal.
You'll be tempted to still add an "amen" even if you do express the meaning rather than the word. If so, that's okay! Remember, Jesus often started his speech using "Amen, amen," so there is nothing to suggest Christians cannot use either an expression of meaning related to "amen," or an expression to God together with "amen," when we conclude our prayers or blessings, in Jesus' name.—John 15:7; 16:23.