Tautochrone
Tau"to*chrone\, n. [Gr. ?, for ? ? the same + ? time: cf. F. tautochrone.] (Math.) 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.