In 1912, a tetrahedron was described as "a geometric shape that includes no more than four equilateral triangles." It was also "a figure with a polygon base and four equilateral triangular faces," or "one of five ordinary solids." A more modern definition of a tetrahedron is "a solid formed with four plane faces."
Are You Brainy Enough to Pass This Vocabulary Quiz?
Education 6 Minute Quiz 6 Min