Pronounced: hap (duh), noun/verb
Notes: You probably think you know the meaning (as did I), but there is one of the verb meanings that I’d not heard before (and so it made the list)
The word fribble means, as a verb, “to act in a foolish, frivolous way” (often followed by ‘away’). As a noun, it is “a fool”
The word came into English in the mid-1600s
Background / Comments
I am pleased with myself about this one: before I looked at the background, I assumed that it came from a corruption of “frivolous”, and that is pretty close to correct: the verb “frivol” is a back-formation from the adjective “frivolous”, and it is assumed that fribble is an alteration (corruption?) of “frivol”.