Tetragrammaton is the original four-letter word. It is a Greek word used by the Early Christian Church (which was Greek-speaking) for the four Hebrew symbols which represent the name of God. The Hebrew names for the four letters are Yod, Heh, Vav and Heh. They can be transliterated into English as YHWH or YHVH; many languages are ambiguous about the distinction between V and W. The Hebrews did not write down vowels, but it is generally now reckoned that the name had two of them and was 'Yahweh'. You can see a good picture of the Tetragrammaton at composer Christos Hatzis's Website.
When Moses asked God for his name, the reply was 'Yahweh'. This appears to be the Jewish God's personal name. But all names originally have a meaning - what does God's name mean? The most likely translation is 'He Who Is', meaning 'the one that exists'. An alternative translation is 'Made-Maker', that is, 'maker of all made things.'
The name 'Yahweh' appears more than 6,800 times in the Hebrew Bible, but in later years the Jews started the custom of never saying the name aloud. It was too holy to be uttered. This may have been a strict interpretation of God's commandment not to take his name in vain. When reading out the holy scriptures, the Jews started using the words 'Elohim' and 'Adonai', which are normally translated as 'God' and 'The Lord.' The name 'Yahweh' continued to be written down, although it was not spoken.
A Special Word For A Special Name
In the 4th Century BC, Alexander the Great of Macedonia conquered the whole of the Near and Middle East. Greek became the language that everybody wanted to learn, much as English is today. Jews living in Egypt no longer spoke Hebrew in day to day life and they wanted a version of the Bible that all literate Jews could read. The Bible was translated into Greek - the first five books in about 250 BC and the rest over the next 100 years or so. This Greek bible was later given the name 'Septuagint,' from the Latin word for 70, because about 70 people were involved in the translation.
The translators of the Septuagint faced the problem of how to translate the four-letter name of God into Greek. They could have chosen to transliterate it into Greek letters, but Greek didn't include the H or V/W sounds of Hebrew, so there were no Greek letters for these sounds. The closest they could get was ΙΑΟΥΕ which is pronounced 'ee-ah-oo-eh'. This was not close enough to the real name for the Jews, so they decided not to translate it at all. Early examples of the Septuagint show that mixed in with the Greek text, the name of God continues to be written in Hebrew, using the four Hebrew letters.
Greeks seeing these four letters made up the name 'tetragrammaton' (four-letter word) and the name stuck.
Removing the Four-letter Word from the Bible
Books which are used from day to day don't last forever, so the early Bibles were copied by hand and new ones produced and used. In about 200 AD, during this copying process, the Greek-speaking Early Christians started replacing the Hebrew YHWH in their Bibles with the Greek word 'Kyrios' which means 'Lord'. Why they did this is not clear. Perhaps, because none of them now spoke Hebrew, it was an embarrassment to them to have a Hebrew word in their Bible. The decision to call God 'the Lord' introduced confusion, as they also used the term 'the Lord' for Jesus, the founder of Christianity. It's not always clear now which Lord they were referring to.
Soon after this, the Roman world adopted Christianity as its official religion and the Bible was translated into Latin. 'Kyrios' became 'Dominus' so the Latin Bible had 'the Lord' right from the start, rather than the name of God.
That piece of halibut was good enough for Jehovah
The true pronunciation of the name 'Yahweh' may have been forgotten or it may have been a secret known only to the Jewish Rabbis. In the period of the 6th to 10th Centuries, a group called the Masoretes tried to reconstruct the name of God from the four letters YHVH. They chose the vowels e, o and a and came up with 'Yehovah,' often written 'Jehovah.' This is a fabrication. Despite its use in Monty Python's The Life of Brian, it is a word that was never known to the Jews.
Nevertheless, 'Jehovah' became the standard pronunciation for the name of God outside of the Jewish world. It appears in many hymns, such as the Welsh favourite 'Guide me, O Thou great Jehovah', more often known as 'Cwm Rhondda'.
One group of Protestants made the name a central part of their belief: the Jehovah's Witnesses. They attempted to restore the true name to the Bible, retranslating it and putting in 'Jehovah', rather than 'The Lord' everywhere the tetragrammaton appeared. They also carried this practice forward into the New Testament, changing 'Kyrios' back to Jehovah. This has led to their somewhat different beliefs about the divinity of Jesus Christ; certain New Testament passages which most Christians think refer to Jesus are considered by the Witnesses to refer to Jehovah, leading to quite a different emphasis.
The Name Restored
In the 19th Century, more enlightened scholars successfully reconstructed the name 'Yahweh', using evidence from many sources. These involve the use of part of God's name in various Jewish names, the pronunciation rules of ancient Hebrew and the pronunciation of the name by the Samaritans, a dissident group of Jews who split from the orthodox Judaism in about 700 BC. They never developed the ban on saying the name, pronouncing it 'Yah-bay'.
The name Yahweh is now normally used in any scholarly discussion of the name, but it is also commonplace in the biggest branch of Christianity: Catholicism. Since the Catholic Church underwent a major revision of practice in the 1960s in the Second Vatican Council, the name Yahweh has been commonly used and is well-known from such hymns as 'Yahweh, I Know You Are Near' and 'To You, Yahweh, I Lift Up My Soul'.
For believers in the Christian God, it is a great comfort to know that they can call him by his own proper name, whether they pronounce it 'Jehovah' or 'Yahweh'.