#Linguistics Modern scholars think this nickname might be a reference to having bad teeth because the tǫnn part means tooth and the blá part meant black or blue. Harald, thus, is known in English as Harald Bluetooth. So there's that.
Harald Bluetooth had a wife named Gunhilde. This was also a very common name. In fact, he also had a daughter named Gunhilde. I don't know the exact meaning, but both bits of that name gave to do with war. +
#Linguistics Eventually, in the 13th century or whatever, someone invented a smaller canon that you could carry. They called it a hand cannon or, colloquially, a hand Guna. This is why we call firearms "gun".
So this one Danish immediate family's names are the origin of two words for technologies that are hallmarks of modern technology: the gun and Bluetooth.
Language is weird.
#Linguistics You know how sometimes we name weapons after women? Like we might paint "Big Bertha" on the side of a giant fuckoff artillery deal mounted on a naval ship?
Well when cannons were newish they did this, too. There was one particular canon that was famous because it was so big and the folks that owned it had named it Queen Gunhilde. So there was a lot of copy catting of that name. And this common name for cannons eventually got shortened to just Guna. +