What's That Flat?

Terminal rotation

A pair of words becomes another pair of words when all four terminal letters shift position, in a manner analagous to rotating tires on a car: each front letter moves to the end, while the back letters move in front and switch words. Examples: tend, bums sent, dumb ; dapper, sought tapped, roughs ; taps, lair rapt, sail .

The terminal rotation was invented by Bartok and introduced in August 1998.