from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A polyhedron with four faces.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. a polyhedron with four faces; the regular tetrahedron, the faces of which are equal equilateral triangles, is one of the Platonic solids.
from the GNU version of the Collaborative International Dictionary of English
- n. A solid figure inclosed or bounded by four triangles.
from The Century Dictionary and Cyclopedia
- n. A solid comprehended under four plane faces; especially, the regular tetrahedron, or triangular pyramid having its base and sides equilateral triangles.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. any polyhedron having four plane faces
Late Greek tetraedron, from Greek, neuter of tetraedros, four-faced : tetra-, tetra- + hedrā, face of a geometric solid.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek τετράεδρον (tetraedron, "triangle-based pyramid"), from τετράς (tetras, "four") + ἕδρα (hedra, "seat"). (Wiktionary)