Cohen is most often a Jewish surname that means "priest; rabbi" in Hebrew. The original Cohens were rabbis descended from Aaron in the bible. Occasionally you find a Cohen who is Irish. Though this name is usually anglicized Coyne or Cowen, Cohen sometimes stands for an anglicization of the Irish surnames Ó Catháin ("wild goose") or Comhdáin, ("shared gift.")As for the Australian aboriginal origin, there are hundreds of aboriginal languages in Australia, and while I can't verify it means "thunder," I can't find that it *doesn't* either! Like American Indian names in the USA, though, if a book can't tell which language or tribe a name is from, it's likely that the information isn't that good.