The Muslim answer holds up. Do not lead with this one.
Some Christian material says Allah was originally a pagan Arabian moon god. It was popularised by Robert Morey's book The Moon-God Allah in 1994.
It is usually linked to the crescent symbol and to the South Arabian god Sin, or to Hubal. The conclusion drawn is that Muslims worship a repackaged idol.
Allah is simply the Arabic word for God. It is the cousin of Hebrew Elohim and Aramaic Alaha.
Arabic-speaking Jews and Christians used it before Islam existed. Every Arabic Bible uses it today.
Genesis 1:1 in Arabic begins: in the beginning Allah created.
Quran 41:37 says "Do not prostrate to the sun or the moon." The crescent came into Islamic use centuries later, through the Ottomans. Morey's archaeological links, including Hubal and the Sin temple at Hazor, are rejected by the specialists in that field.
Not only Muslims. Rick Brown published the refutation in the International Journal of Frontier Missions in 2006.
Christian scholars of mission have done this work themselves. This is our own house correcting itself.
If you use it, any informed Muslim wins in one sentence, and your stronger arguments die with it. The real dispute is about God's character and his triunity, not about the Arabic word for him.
Drop the argument, keep the question.
"I have heard Christians say Allah is a moon god. That is not true, and I will not say it."



Allah is just the Arabic word for God, and Arab Christians used it first.
The rebuttal here is not a Muslim reply but the evidence itself. Scholars across the field grant it. That includes Christians who study mission. Allah is the ordinary Arabic word for God. It is the cousin of Hebrew Elohim and Aramaic Alaha.
Arabic-speaking Jews and Christians used it before Islam. It appears in every Arabic Bible to this day. Genesis 1:1 in Arabic begins: in the beginning Allah created. The Quran flatly bans worship of the moon. Do not prostrate to the sun or the moon (41:37). The crescent came into Islamic use much later, through the Ottomans. And Morey's links to old sites are rejected by the experts in that field. Those links include Hubal and the Sin temple at Hazor.
Do not use this one: it is false, and an informed Muslim wins at once.
Weighed fairly, this criticism fails. The language settles it. Allah is the standard Semitic word for God, used by Christians before Islam and in Arabic Bibles now. So does the Quran's own ban on worshipping the moon.
Rick Brown published the refutation in the International Journal of Frontier Missions in 2006. Christian scholars of mission have done this work themselves. The real dispute with Islam is about God's character and his triunity, not about the Arabic word for him.
Christians who use the moon-god argument hand every informed Muslim an easy win, and discredit their stronger arguments with it. It is marked answered so that you never make this mistake.