HYPOTROCHOID

Etymology

Noun

hypotrochoid (plural hypotrochoids)

(geometry) A geometric curve traced by a fixed point on the radius line outside one circle which rotates inside the perimeter of another circle.

Source: Wiktionary

Hy`po*tro"choid, n. Etym: [Pref. hypo- + trochoid.] (Geom.)

Definition: A curve, traced by a point in the radius, or radius produced, of a circle which rolls upon the concave side of a fixed circle. See Hypocycloid, Epicycloid, and Trochoid.

Source: Webster’s Unabridged Dictionary 1913 Edition