To widdle = to urinate. At least that's what it means in Yorkshire.

We also say 'tiddle', which has the same meaning.

In the UK it means urination. But as the answer above demonstrates it is not known by all native speakers. In fact it might be exclusive to the UK.

The only thing that comes to mind is "whittle" which is the act of carving wood. Otherwise widdle doesn't mean anything. Unless a child is saying "widdle" instead of "little." :)