It’s right here in the Wikipedia, says Richard Johnson. “The word ‘God’ in English is ultimately derived from the Proto-Indo-European word ‘Ghu’!”
Ghu, of course, is the satirical deity invented by 1930’s science fiction fans.
The ulterior etymology is disputed. Apart from the unlikely hypothesis of adoption from a foreign tongue, the OTeut. “ghuba” implies as its preTeut-type either “*ghodho-m” or “*ghodto-m”. The former does not appear to admit of explanation; but the latter would represent the neut. pple. of a root “gheu-“. There are two Aryan roots of the required form (“*g,heu-” with palatal aspirate) one with meaning ‘to invoke’ (Skr. “hu”) the other ‘to pour, to offer sacrifice’ (Skr “hu”, Gr. ???i;?, OE “geotàn” Yete v).
So that, as clear as is the summer’s sun.
[Thanks to Bjo Trimble for the story.]