Definition of pyramid
1 a
: an ancient massive structure found especially in Egypt having typically a square ground plan, outside walls in the form of four triangles that meet in a point at the top, and inner sepulchral chambers
b
: a structure or object of similar form
2
: a polyhedron having for its base a polygon and for faces triangles with a common vertex — see Volume Formulas Table
3
: a crystalline form each face of which intersects the vertical axis and either two lateral axes or in the tetragonal system one lateral axis
4
: an anatomical structure resembling a pyramid: such as
a
: any of the conical masses that project from the renal medulla into the renal pelvis
b
: either of two large bundles of motor fibers from the cerebral cortex that reach the medulla oblongata and are continuous with the pyramidal tracts of the spinal cord
5
: an immaterial structure built on a broad supporting base and narrowing gradually to an apex
- the socioeconomic pyramid
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