I don't have any mega-dictionary to hand, but will 'ask a friend'. In the meantime I looked in my only grown-up English dictionary, which happens to be the Canadian Oxford English D and there's no 'tump' in it.

There is, however, 'tumpline' which apparently is the strap slung across the forehead or the chest to support a load carried on the back. 'Tump' being an alteration of mattump, which is supposed to be of Southern New England Algonquian origin.

Now, see! Madoc discovered America, everyone knows that, and the Mandan native americans were his descendants so obviously they referred to the pack/hump on Madoc's back, when trekking, as 'Madoc's tump which became 'Mattump'.

I think I could now create a mathematical equation proving that a backpack = Traffic Warden ...

sian