Webster's Revised Unabridged Dictionary · 1913

Folium

Folium , noun

[Latin, a leaf.]

1.
A leaf, esp. a thin leaf or plate.
2.
(Geometry) A curve of the third order, consisting of two infinite branches, which have a common asymptote. The curve has a double point, and a leaf-shaped loop; whence the name. Its equation is x3 + y3 = axy.