A mutton-headed what??

...mugwump, is how Boris Johnson described Jeremy Corbyn the other day.  Not an every-day word these days, although I remember it being common currency when I was at school back in the early 50s.  My recollection is that it meant someone who couldn't (or couldn't be bothered to) make up their mind about something and therefore sat on the fence with their mug hanging over one side, and their wump - which I always assumed was their backside - hanging over the other.  Whether this was the sense in which Boris meant it, I'm not sure but if you Google it, you will find that the word has its origins in a native American word meaning "great warrior" or something similar, and I'm pretty sure he didn't mean it in that sense.  So for the moment  it remains somewhat of a mystery.