The root of the word comes from Hebrew aman, which means to nourish and make strong. Emunah (faithfulness) also comes from aman. The ancient Greeks used the word (AMHN) from Hebrew to mean 'truth', 'surely', 'absolutely'. It is one of just a few Hebrew words which have been imported unchanged into Church liturgy. The current meaning of Amen and its pronunciation is pretty much the same in any modern language and religion.
Christians say either 'Ahh-men' or 'Ay-men'.
The 'Ahh-men' pronunciation tends to be a bit more formal and used in liturgy, choral music, etc. An example can be heard in the closing part of Handel's Messiah 'Worthy is the Lamb'3. The Ahh-men in the final chorus is repeated dozens of times, runs to six pages in a typical choral score, and usually takes around 3 minutes 40 seconds to sing.
The 'Ay-men' pronunciation is often associated with evangelical Christians and Gospel singing. Unlike Handel's Messiah, the Gospel chorus 'Amen' has only five words, all the same (Ay----men, Ay----men, Ay----men, Ay-men, Ay--men.) yet can take much longer to perform as it is repeated over and over again, bringing the congregation into harmony.
For Jews, Amen is also an acronym for El Melech Ne'eman, which means "Mighty, Faithful King".
Muslims use Amen (Amin or Ameen) in the same way as Christians and Jews, even though the word does not appear in the Qur'an. Muslims say it after reciting Surah al-Fatihah, after completing their prayers, at the end of letters, etc.
Buddhists and Hindus
Many Buddhists and Hindus also use Amen at the end of prayers and as concurrence in the same way as the other religions.
But where did it all begin?
From old Egyptian texts we can see that people regarded the sun as the emblem of the Creator. They called the sun Ra, and all other gods and goddesses were forms of the Creator. One of these gods was Amen; a secret, hidden and mysterious god named variously Amen, Amon, Amun, Ammon and Amounra. For the first eleven dynasties (c. 3000-1987 B.C.) Amen was just a minor god, but by the 17th dynasty (c. 1500 B.C.) he had been elevated to be the national god of southern Egypt. This position gave Amen the attributes and characteristics of the most ancient gods, and his name became Amen-Ra, that is, a supreme form of God the Creator. By the 18th Dynasty (1539-1295 B.C.) a college had been established to study Amen-Ra and as a focal point for worship.
Jews settled in Egypt for around 400 years4 from 1847 B.C. and during this sojourn they would certainly have been fully exposed to the worship of Amen-Ra. By the time of their exodus from Egypt in 1447 B.C., the term 'Amen' would be in their language even if it was not their god. It would be a word that had associations with reverence and majesty. This is not difficult to understand. People still talk about Moses, Jesus, Mohammed and Buddha, and often use those names completely out of context as expletives. Amen was seen as a powerful god and the name continued, out of context, as an exclamation or salutation; a classic example of language evolution. From the Jews, the word was adopted by Christians, Muslims and others.
So Amen was originally the name of a Pagan god, who was considered a form of God the Creator. But he was certainly not considered God, or Christ. Interestingly, most Pagans today tend not to use the word, preferring instead to say "So mote it be", an old Anglo-Saxon term. Perhaps they see the word Amen in the Bible and the Tanakh and don't want to be associated with Christianity or the like. Indeed, in the Bible5 we see Jesus Christ referred to as "The Amen". Christ is God's Amen to all that he has spoken. Thereby the name used for an old Egyptian god is replaced by the same name used for Christ.
Like many other words used in religion, (or art, mathematics, medicine, etc.) it's easy to believe that our ancestors saw no point in creating new vocabulary when existing and familiar words could be recycled. (The term 'God', for example, has been recycled by most religions.) Yet some people are vehemently protective of things and believe Amen is a biblical word which is also found in the Tanakh and in Islam, and happens to sound like the name of a Pagan god. Others believe it is an Islamic word that can also be found in the Bible and Tanakh. And so on. The whole issue is hotly debated and any Pagan link denied by many. Who knows how many accidental or deliberate mistranslations have crept in over the centuries.
Those who believe that God is the Great Mathematician will no doubt point to the numeric value of Amen:
"Finally, we may note that the word Amen occurs not infrequently in early Christian inscriptions, and that it was often introduced into anathemas and gnostic spells. Moreover, as the Greek letters which form Amen according to their numerical values total 99 (alpha=1, mu=40, epsilon=8, nu=50), this number often appears in inscriptions, especially of Egyptian origin, and a sort of magical efficacy seems to have been attributed to its symbol."
(Catholic Encyclopedia Vol. 1; 1907)
Nowhere in the Bible, the Tanakh or the Qur'an can we find words to suggest one can be redeemed by merely uttering a magic word.
Whether Amen is magic, rooted in a Pagan deity, originally a Christian word, a Muslim word, a Jewish word, or anything else, the question is the same: So what? When Christians, Jews and Muslims say Amen, they do not invoke any god or any power just by saying that word or indeed any other word. Amen does not even make other words more sincere. But Amen, like all the other language we use, helps us to focus on what we mean in our hearts.
And that is the answer to "So what?" What really matters is what is said by the heart.