Tautochrone
Tautochrone , noun
[Greek {not transcribed}, for {not transcribed} the same + {not transcribed} time: compare French tautochrone.]
(Mathematics) A curved line, 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; as, an inverted cycloid with its base horizontal is a tautochrone.