Fo·li·um n.; pl. E. Foliums L. Folia
1. A leaf, esp. a thin leaf or plate.
2. Geom. 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.
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folium
n : a thin layer or stratum of (especially metamorphic) rock
[also: folia (pl)]