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n. pl. tris·oc·ta·he·drons or tris·oc·ta·he·dra (-drə)
A solid figure having 24 equal faces, every three of which correspond to one face of an octahedron.

[Greek tris, thrice; see trei- in Indo-European roots + octahedron.]

tris·oc′ta·he′dral (-drəl) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


n, pl -drons or -dra (-drə)
(Mathematics) a solid figure having 24 identical triangular faces, groups of three faces being formed on an underlying octahedron
[C19: from Greek tris three times + octahedron]
trisˌoctaˈhedral adj
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(trɪsˌɒk təˈhi drən)

n., pl. -drons, -dra (-drə).
a solid bounded by 24 identical faces in groups of three, each group corresponding to one face of an octahedron.
[1840–50; < Greek trís thrice + octahedron]
tris•oc`ta•he′dral, adj.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
The following forms were identified: the rhombic dodecahedron, the pyritohedron, the trapezohedron, several dyakis dodecahedra, and probably the triakis octahedron [= trisoctahedron], Wagner stated that the Tweefontein sperrylite crystals are typically 1.3 mm to 1.7 cm in size.