noun, plural tet·ra·he·drons, tet·ra·he·dra [te-truh-hee-druh] /ˌtɛ trəˈhi drə/.
Examples from the Web for tetrahedron
The tetrahedron in Fig. 32 may appear either as erect on its base or as leaning backward with its base seen from underneath.Visual Illusions|Matthew Luckiesh
Round Mars describe a tetrahedron; the circle including this will be Jupiter.
From the sides of the hollow square sprang long arms of spheres, each tipped by a tetrahedron.The Metal Monster|A. Merritt
About Mars' orbit describe a tetrahedron: the sphere containing this will be Jupiter's orbit.The Life of Galileo Galilei, with Illustrations of the Advancement of Experimental Philosophy|John Elliot Drinkwater Bethune
That for the tetrahedron has 12 for its order, for the cube (or octahedron) 24, and for the icosahedron (or dodecahedron) 60.
British Dictionary definitions for tetrahedron
noun plural -drons or -dra (-drə)
Word Origin for tetrahedron
Word Origin and History for tetrahedron
solid figure contained by four triangular surfaces, 1560s, from Late Greek tetraedron, originally neuter of tetraedros (adj.) "four-sided," from tetra- "four" + hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit" (see sedentary).