Allah is the name of God, and has connotations of there being none worthy of being worshipped and none having the right to be worshipped in truth except He.
So when he came to it, he was called from the right side of the valley in a blessed spot - from the tree, "O Moses, indeed I am Allah, Lord of the worlds." (Qur'an 28:30)
Here you can see Allah introduces Himself by His name, and then describes who He is with a beautiful description.
O Moses, indeed it is I - Allah, the Exalted in Might, the Wise." (27:9)
And again in the above.
Indeed, I am Allah. There is no deity (none worthy of worship) except Me, so worship Me and establish prayer for My remembrance. (20:14)
is 'Allah' the name of the one monotheistic god
Yes.
or Allah is simply a title for gods, as in Venus could be considered a female version of it in roman mythology?
No. There are no versions of Allah.