Crown
Cap
Your forehead is the origin for the measurement for your crown! If you measure somewhere else on your head for a crown it won't fit.
かん
かんむり
None
You want your crown to be just like Genghis Khan's (かん), which was more of a cap. He's your hero though, because he ruled over the most people, so you want yours to match his measurements.
An update is needed before you can continue but you have more than one WaniKani tab open.
Finish up what ever you are doing on the other tab(s), then close them to continue.
The update will complete automatically once the other tab(s) are closed.