And I put derby for the England clue. I believe I am right that the hat is named after a town in England. And it's five letters! Just checked the hat is from England and that's probably why Americans called it a derby. It was worn by Billy the kid and other outlaws because it didn't fall off in wind and when riding horses
Here's some more...
Danube River/delta in Europe. Dundee city in Scotland. Countries beginming with "d". D.r., Denmark, Congo, Dominica.