TAUTOCHRONE
Etymology
Noun
tautochrone (plural tautochrones)
(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.
Source: Wiktionary
Tau"to*chrone, n. Etym: [Gr. tautochrone.] (Math.)
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition