Definition of "tourbillon"

Time was vulnerable to the force of gravity. So Breguet came up with the tourbillon, which isolated the balance wheel and escarpment off on a little platform of their own, geared to the third wheel, rotating about once a minute, assuming in the course of the day most positions in 3-D space relative to the gravity of the Earth, so the errors would cancel out and make time impervious to gravity.

2006, Thomas Pynchon, “Bilocations”, in Against the Day, New York, N.Y.: Penguin Press, page 457

In their final year, each student must make their own watch with a complication—from a tourbillon to a chiming mode to having a date display.

2023 May 28, Brian Ng, “Is one of these students the next Breguet?”, in FT Weekend, HTSI, page 43