The word 'bobble' originated as the frequentative of the verb 'to bob' -- that is, 'to bob over and over'. More specifically, to bobble is 'to move or handle something with continual bobbing motion'. Despite having such a seemingly straight-forward meaning, it is a quite confusing word, even for the English language.

Bobble is used in a number of senses; one could bobble a catch (i.e. drop the ball), run into a bobble in your boat (a rough patch of water), knit a bobble (a raised bump of stitches, especially when repeated), or to bob back and forth. However, one would not say that one "bobbles ones head to the music" (that would be 'bob'), or that one "bobbles on the sea" (again, we would use 'bob').

As a matter of fact, the sense of 'to bob frequently' exists most commonly in the adjective form, when referring to a 'bobblehead doll', a figurine with a head that continuously bobs back and forth (European readers may recognize them by the name 'nodder doll'). Obviously, this is not a term frequently used, and while most English speakers will still recognize 'bobble' as a word, is it steadily being marginalized to the realm of brand names and technical jargon.