Main Entry: ¹pyr·a·mid

Pronunciation: \ˈpir-ə-ˌmid\

Function: noun

Etymology: Latin pyramid-, pyramis, from Greek

Date: 1549

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 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: as a : any of the conical masses that project from the renal medulla into the kidney 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>

— py·ra·mi·dal \pə-ˈra-mə-d^əl, ˌpir-ə-ˈmi-\ adjective

— py·ra·mi·dal·ly adverb

— pyr·a·mid·i·cal \ˌpir-ə-ˈmi-di-kəl\ adjective

[pyramid illustration]