Coronet?! Who uses this word? How bout "crown"?
Sometimes duo's priorities of which words to teach are a bit... arbitrary.
I'm an English speaker learning German, and I would sooner recognize/understand Krone than I would "coronet".
Good question. I've mostly seen the term in historical novels that are rife with royalty. Apparently it's a sort of lesser crown--for princes and the like who are outranked by the sovereign. See: http://www.merriam-webster.com/dictionary/coronet