The etymology of this word comes from an invisible proto-language. If you're confident you know the etymology, feel free to add it, but reader beware should the etymology be added by someone other than the creator of the language!
The similarity to Dothrakiao was intentional. First, I really liked the sound, and I liked it as a pronoun—and specifically a second person pronoun. It sounded good to me to refer to someone using ao. Second, I thought it was a nice way to demonstrate that Dothraki and High Valyrian were different languages. There was no way to tie the etymologies together and suggest the two words came from a common source.