Everywhere you search whether it be Google or Youtube regarding bobbleheads, everyone spells it different. The word “bobble” is an actual word. Many people spell it as “bobblehead or bobble head”. I’ve been known to spell it both ways as well. So for some clarification here ya go. 

According to dictionary.com the definition of bobble is as follows:

1. a repeated, jerky movement; bob.
2. a momentary fumbling or juggling of a batted or thrown baseball.
3. a repeated “bobbing” movement
So for you English scholars, both “bobble” and “head” are actual words. When you combine both words together (bobblehead) it turns it into a “compound” word, which is the combination of two words in one. 
Either way you want to spell it, I can give two smelly shits. Although, I do get a kick out of some of you who spell it either bobblehead or bobble head. Technically, the correct way to spell it is “Bobblehead”. There’s your Language Arts lesson for the day.