The oldest known form of Israel's Covenant name of God,
(As found in the Dead Sea Scrolls, read right to left above blue arrow).
Note the difference between the old Hebrew script of the Name and the square Jewish script on either side. The later square script arose from Aramaic [Gentile] influence.

name Yahweh (sometimes translated as Jehovah or LORD) is the principal name used for God in Old Testament writings. It is uniquely Israel's name for God. It was used for God before Moses (as its abbreviation in a component of the name of Moses' mother indicates), even as far back as the Hebrews from whom Abraham came, as Laban's words show (Gen.24:31), but it was not a vehicle of God's self-revelation until God called Israel out of Egypt into a national covenant with Himself.

God explained to Moses in Exodus 6:3 –

"I appeared to Abraham, Isaac, and Jacob, as God Almighty [El Shaddai],
but by My name, Yahweh (YHWH), I did not make Myself known to them."

The Hebrew script did not indicate vowels until about the ninth century AD and so there has been some conjecture about the pronunciation of YHWH, but Clement of Alexandria in the second century AD used the form Yahweh and other Greek transcriptions also indicate this same pronunciation. 

The pronunciation had been confused by the technical reverence that developed in synagogue reading from about the third century BC of saying adhonai (master/lord) when reading YHWH.  (Ignorance of this led the translators of the 1611 King James Version of the Bible in error to translate the consonants of Yahweh with the vowels of Adonai to produce the name 'Jehovah'). Today this same technical avoidance of taking the Lord's name in vain is often seen in spelling of God as G-d. This is not quite what this Sinai commandment had in mind.

Strangely, scholars of the last two centuries have based a whole theory of the origin of the Old Testament scriptures on these two principal terms for God in Israel's Bible. The so-called Yahwist sources (which used the term Yahweh) and the Elohist sources (which used the term Elohim). On the basis of this presupposition then the Bible is divided up in an attempt to find the scraps of supposed previous documents on which the sacred Scriptures are conjectured to have been based.

the simple difference of emphasis provided by these two terms (Yahweh/LORD and Eloihim/God), rather than being competing synonyms from different sources, is well illustrated in the Bible's own report on how a king cried to God in desperation and was helped. The term Yahweh is used with reference to God's personal relationship, and the term Elohim is used with reference to God's sovereignty over all in this example of the Hebrew parallelism in Semitic thought:

For this reason, the term Elohim is used in Genesis to describe the overall creative acts of the Most High (Genesis 1), and the term Yahweh is added or used as an alternative when the acts of God involve a personal relationship (Genesis 2). These two terms are simply complementary and never indicate competing narratives.

Our ignorance of the pre-Israelite history of the Hebrews has lost any certainty for us concerning the primary grammatical significance of YHWH, but the manner of its use by God in communicating its special significance to Moses, cited above, together with aspects of Hebrew grammar, gives us a clue which seems confirmed in our New Testament.

In other words, in YHWH is simultaneously the past, the present, and the future! Or, as the French translation gives – l'Eternel.

So, a legitimate translation would be the "Ever-Present-One",

or as the Bible itself describes:

was often abbreviated as 'Yah' or 'Jah' (Ps.68:4, "His name is Jah"). Sometimes used (poetically) in conjunction with the full term, as in the first reference to the Lord in Ex.17:16 ("throne of Jah").

However, Jewish scribes, first in Palestine and later in Babylon gradually dropped the 'dagesh' accent in the audible 'h' in its short form (central 'h' in its full form) so that it became inaudible and was no longer treated as a separate word-equivalent of Yahweh (Ginsburg, Massorah vol.4,p.472,§160).

This probably occurred as part of the process of sacralizing the term Yahweh to its exaggerated status in Judaism and in the pseudo-Christian 'Sacred Name Movement', as almost worthy of worship in itself: another bizarre twist in the human history of spiritual deviance.

This sad influence continues in various forms of Judaized Christianity today in which the Hebrew characters of 'Yahweh' are inserted into English text of the Bible without translation or even transliteration (by the Institute for Scripture Research 1998 translation) as though it were some special mark of reverence.

The equivalent in its short form however appears in human names as a devotion (Moses' mother, etc.); in the worship word usually transliterated into English as 'hallelujah'; and even in a place name 'Bizyothjah' ("contempt of Jah"), a city in Judah (Jos.15:28).