While it appears that GoTo.com
purchased a company called Cadabra in late 1999, that doesn't seem to satisfy the criteria of the question.
It seems that GoTo.com and Cadabra existed simultaneously but independent of one another, suggesting that Cadabra wasn't GoTo.com's original name, but simply a company that they purchased.
However, as
this link shows, Amazon.com CEO Jeff Bezos originally intended to name his endeavor Cadabra.
So, take that for what you will.