The turnover of names for God in the
Jewish religion is a classical example of
taboo in language. Any word that comes in to replace the taboo word itself acquires taboo and has to be replaced again. Because the Judaeo-Christian tradition is so central to Western culture, it presents a rather confused picture if you look only at
Hebrew names.
However, historically Hebrew is only one among many closely-related Semitic languages. It is very close to Phoenician, Canaanite, Aramaic, and many other extinct but well-understood languages, and more distantly related to Arabic and the extinct Mesopotamian languages like Akkadian and Babylonian. So the original meanings and forms of Hebrew words can often be reconstructed with great confidence by comparing them to other languages where the taboo hasn't been anywhere near as prominent.
In what follows I'm going to use ? for aleph, the glottal stop consonant (that really is a question mark, it's not some peculiar thing that your browser can't render), and & for ayin. To get back to ordinary-looking transcriptions, just leave them out or replace them with an apostrophe.
What we see then is this: ?adon and ba&al were Semitic words for lord or master, and ?il or ?ilah was the ordinary word for god, any god. The personal name for the Hebrew god was written yhwh at a time when only consonants were written, so it's not clear how it was pronounced. In the early days the Hebrews were henotheist, that is they only worshipped one god, their own, but didn't deny the existence of the gods of other peoples.
Now to expand on that. Under the node Adonai, ariels correctly says it is plural in form, "my lords": ?adon 'lord', ?adonim 'lords', ?adoni 'my lord', ?adonay 'my lords'. Grammarians call this the pluralis majestatis "plural of majesty", because it seems to be singular in meaning. The word Elohim is likewise plural in form but singular in meaning. These do not, in the Hebrew Bible, imply gods, plural -- though that is not to exclude the possibility that they derive from an earlier stage when there was a plurality of gods. As well as being the general word for lord or master, it was used in some cultures for the names of a particular god: Adonis, and later the Jewish god when the name Yhwh was replaced.
Baal or Bel is another word for lord or master, common in Semitic languages, and which also has been understood as the name of particular Semitic gods, though not the Jewish god. I don't know what the original difference between ?adon and ba&al was. The Hebrew words for 'husband' were ?ish 'man' and ba&al.
The general Semitic word for a god is either a monosyllable ?il or ?êl (the interchange between the two vowels is standard), or a disyllable something like ?ilah: for example Akkadian ?ilahu, Arabic ?ilâhu. (The final -u is a case ending, which Hebrew has lost.) The connexion between ?il and ?ilah is unclear: there are no precedents for either lopping off the second syllable or adding it as a suffix. (It is not the same as the common Semitic feminine ending -ah.)
The familiar Arabic name Allah contains al- 'the'. The Arabic for 'the god' in general is al-?ilâhu, and for the one god of monotheism is allâhu, a contraction of it.
The Hebrew form of this word 'god' is ?êl, but this does not (to my knowledge) occur in isolation1, though in the form el it occurs in many Biblical names, such as Michael, which is mi kha ?êl 'who is like God?'. In the longer form ?eloh- (with shortened first vowel) it always occurs in the plural ?elohim. As with ?adonay this is a pluralis majestatis and does not necessarily imply real plurality. The noun ?elohim is plural but the verb agreeing with it is singular.
Also, it is used as a name: the first statement of Genesis is brêshit bârâ ?elohim ?êt-hashshâmayim w?êt-hâ?âresz 'in beginning Elohim made the skies(sky) and the earth': i.e. there is no 'the' on Elohim. It would have been perfectly possible to say hâ?elohim if it had meant 'the gods'.2
The personal name Yhwh is usually supposed to have represented Yahwe. I don't know what this assertion is based on. I don't know whether there were other Semitic gods with similar names. (Immanuel Velikovsky built up a theory that it was the sound of the planet Venus rushing by... or something... we draw a discreet veil over that and resume serious discussion.) Anyway, the second H was probably silent. The consonant H is usually silent at the end of a Hebrew word: it was a way of writing long vowels. (When it was actually pronounced H they put a dot inside it.) So, Yahwe is slightly more accurate than Yahweh.
It was not ever pronounced Jehovah, or anything resembling Jehovah. The name Jehovah comes from taking the consonants of Yahwe and replacing the vowels with the vowels of Adonay. It is a purely written construction, because of the taboo on saying Yahwe. The ancient Hebrew texts were sacred and could not be changed: they were written with consonants only. When, because of changes in the language (and Hebrew at one time was a living language like any other), the text did not reflect the spoken language, marginal notes were put in to indicate the actual pronunciation. These were called ktib-qrê 'written-read'. A few of them were so common that they didn't need to be annotated every time, they were just "taken as read".
One of these was the name of God. Wherever it was written Yhwh, it was understood that you said ?adonay 'lord' instead3. The vowels were a later invention, marks written around and inside the consonants. They weren't sacred. They couldn't change Yhwh, but they could write the vowels of ?adonay inside them, giving yahowah. Actually the first vowel is the neutral vowel or schwa, which was a-like in ?adonay and would be e-like in yahowah if the word existed, which is why if you read it off as if it were a real word you get Yehowah, not Yahowah.
In Classical Latin, J was pronounced Y, and V was pronounced W. Hence "Yehowah" was written "Jehovah" in Latin. The change to the modern English pronunciation has got nothing to do with Hebrew. (The letter W is now also pronounced V in Modern Hebrew, but this is unconnected with Biblical Hebrew pronunciation.)
1. Thanks to
arieh for mentioning it does occur bare in
Exodus 6:3.
2. While we're on the absence of articles, the word brêshit 'in (the) beginning' is interesting. In the original consonant text you can't tell whether there's a "the" in it: b-ha-rêshit 'in-the-beginning' contracts to barêshit with the same consonants as b-rêshit 'in beginning'. Normal Hebrew grammar should use the "the". Yet the vowelled text actually leaves it out. It is not clear what difference that made.
3. Except where the original text says Adonay Yhwh, in which case the Yhwh is vowelled and read as Elohim -- thanks again, arieh.