Horch was, in fact, the name of the original head of the company, August Horch. He, essentially, was punted out of his own company by his supposed companions. So, he started a NEW company, August Horch Automobilewerke. But, the first company sued him for trademark infringement. So, he needed to come up with a new name. His son, a student of Latin, suggested Audi...and thus it went.
Horch is the German form of 'hark', meaning to listen, the Latin for of which is, of course, Audi.

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Gott's Leetle Feesh in Trousers!