tetrahedron

noun

tet·​ra·​he·​dron ˌte-trə-ˈhē-drən 

plural tetrahedrons or tetrahedra ˌte-trə-ˈhē-drə 

: a polyhedron that has four faces

Illustration of tetrahedron

Did you know?

The simplest tetrahedron is made of four equal-sided triangles: one is used as the base, and the other three are fitted to it and each other to make a pyramid. But the great pyramids of Egypt aren't tetrahedrons: they instead have a square base and four triangular faces, and thus are five-sided rather than four-sided.

Example Sentences

Recent Examples on the Web

One group started chipping away at the foam volleyballs while another set about taping together basketballs into a tetrahedron. —IEEE Spectrum, 16 Nov. 2020

Mold that box into a pyramid or tetrahedron or any other everyday polyhedron. —Devin Powell, Discover Magazine, 20 Mar. 2019

That extraordinary hardness arises from a strong and inflexible structure: Five atoms form a tetrahedron and share electron pairs with each other. —Gemma Tarlach, Discover Magazine, 5 Apr. 2018

Many elements overlapped, forming a multidimensional sculpture: a triangle might jut out of a tetrahedron and meet another triangle at a point. —Kelsey Houston-edwards, Scientific American, 21 Sep. 2022

If the regular tetrahedron doesn’t tile space, the question becomes: Do any tetrahedra? —Quanta Magazine, 9 Feb. 2021

Triangles and tetrahedra are examples of more general shapes called simplices, which can be defined in any dimension. —Quanta Magazine, 13 Jan. 2015

That extraordinary hardness arises from a strong and inflexible structure: Five atoms form a tetrahedron and share electron pairs with each other. 3. —Gemma Tarlach, Discover Magazine, 23 Mar. 2018

With eight modules of tetrahedrons (triangular pyramids) made of translucent polyethelene and aluminum tubes that billow out from a symmetrical axis, the piece feels both organic and machinelike. —Molly Glentzer, Houston Chronicle, 10 Jan. 2018

See More

Word History

Etymology

New Latin, from Late Greek tetraedron, neuter of tetraedros having four faces, from Greek tetra- + hedra seat, face — more at sit

First Known Use

1570, in the meaning defined above

Kids Definition

tetrahedron

noun

tet·​ra·​he·​dron ˌte-trə-ˈhē-drən 

plural tetrahedrons or tetrahedra

-drə

: a polyhedron that has four faces

tetrahedral

-drəl

adjective