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; and dapper, sought, tapped, roughs; and taps, lair, rapt, sail.
The terminal rotation was invented by Bartok and introduced in August 1998.