Source : Webster's Revised Unabridged Dictionary (1913)

Lemniscata \Lem`nis*ca"ta\ (l[e^]m`n[i^]s*k[=a]"t[.a]),
Lemniscate \Lem*nis"cate\ (l[e^]m*n[i^]s"k[asl]t), n. [L.
   lemniscatus adorned with ribbons, fr. lemniscus a ribbon
   hanging down, Gr. lhmni`skos.] (Geom.)
   A curve in the form of the figure 8, with both parts
   symmetrical, generated by the point in which a tangent to an
   equilateral hyperbola meets the perpendicular on it drawn
   from the center.