HaShem - The Name. In yesteryear, God's Name was (and is) too Holy to be spoke or even written hence God was referred to HaShem - The Name.
Our Bible today, is a translation of the contents of 5 old books known as Codex. They are available to view online or to visit in museums. These form the doctrinal linchpin for Christianity.
Early Christianity did not have the advantage of a Bible with its theology all debated and agreed. To bring commonality to the core of Christianity the 'Nicaea Creed' statement was agreed at the First Council of Nicaea in 325.
In Hebrew the word 'Emunah' has a similar spelling to the word 'Amen' but over the years the meaning has diminished.
The 'amen' has been used at the end of a prayer as a prayer terminator with a response of 'amen' to signify an agreement to the prayer.