Source : Webster's Revised Unabridged Dictionary (1913)

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