How does one define the difference between Cocoa, and Coca?

I had, long, thought that Cocoa was the primary ingredient in chocolate, while Coca was a common name for Cocaine.

Recently, though, a neighbor told me that Coco is the primary ingredient, in chocolate, and that Cocoa is a real name, for Cocaine.

Which of us is "right"?

Also, is there ANY truth to the rumor that Coca Cola was, originally, made, with Cocaine, and that this is the reason why it is called "Coca Cola"?

If un-true, where did such a stupid rumor start?