(mathematics) A curvedline, such that a heavy body, descending along it by the action of gravity, will always arrive at the lowest point in the same time, wherever in the curve it may begin to fall.
Examples
An inverted cycloid with its base horizontal is a tautochrone.
Of course, once the shape of the tautochrone had been determined, the problem of forcing a pendulum bob to oscillate along such a curve remained.
