I have a house I love, and land I love, which may be utterly useless?

Thank you for the clarification. Yes, a ditch then.

Oh, and in a non-permaculture thing, I'm going to build myself a dining table. That ought to be a good set of work for a week.

A swale on contour is as near level as possible, but Swales are not invariably on contour. You can make Swales that are meant to move water away, not just hold it for infiltration.

Geoff Lawton definitely stresses that swales must be on contour. This may be one of those words permaculture has it's own, more specific meaning (like sector).

Swale (landform)

The swale concept has also been popularized as a rainwater harvesting and soil conservation strategy by Bill Mollison, Geoff Lawton and other advocates of permaculture. In this context it usually refers to a water harvesting ditch on contour. Another term used is contour bund.[3][4]

I'm curious, Peter, how you would explain the difference between a swale and a ditch if they can both direct water?