http://www.muslim.org/islam/allah.htm
wrong!!
Contrary to popular belief, the word Allah is NOT a contraction of al-ilah (al meaning 'the', and ilah meaning 'god').
Had it been so, then the expression ya Allah ('O Allah!') would have been ungrammatical, because according to the Arabic language when you address someone by the vocative form ya followed by a title, the al ('the') must be dropped from the title. For example, you cannot say ya ar-rabb but must say ya rabb (for 'O Lord'). So if the word Allah was al-ilah ('the God'), we would not be able to say: ya Allah, which we do.
Lane's Arabic-English Lexicon (which is based on classical Arabic dictionaries), says under the word Allah, while citing many linguistical authorities:
"Allah ... is a proper name applied to the Being Who exists necessarily, by Himself, comprising all the attributes of perfection, a proper name denoting the true god ... the al being inseparable from it, not derived..."
Allah is thus a proper name, not derived from anything, and the Al is inseparable from it. The word al-ilah (the god) is a different word.