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tetrahedron (n.)[tetrahedron 词源字典]: "triangular pyramid, solid figure contained by four triangular surfaces," 1560s, from Late Greek tetraedron, noun use of neuter of tetraedros (adj.) "four-sided," from tetra- "four" (see tetra-) + hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit" (see sedentary). Related: Tetrahedral.[tetrahedron etymology, tetrahedron origin, 英语词源]
leucite: "A potassium aluminosilicate mineral, crystallizing in the tetrahedral system and typically found as grey or white glassy trapezohedra in volcanic rocks", Late 18th century: from Greek leukos 'white' + -ite¹.