Number & MeasureGreek → English
Icosahedron
/ˌaɪkəsəˈhiːdrən/noun
A solid with twenty triangular faces, the most complex of the five regular polyhedra.
The Greek roots
εἴκοσι
eíkosi
twenty
ἕδρα
hédra
seat, base
Literally: “twenty seats”
The story of the word
Plato gave this one to water in the Timaeus, reasoning that the solid closest to a sphere would be the one that flows. Nature agreed in an unexpected place: a great many viruses build their protein shells as icosahedra, because that shape wraps the most volume using identical pieces. The word reaches English in the 1560s, straight out of the geometry books.
- How it travelled
- Ancient Greek → Latin → English
- First recorded
- 1560s
The same roots elsewhere
Other languages reached for exactly the same Greek pieces.
Same family
dodecahedronoctahedronpolyhedroncathedral
In a sentence
The twenty-sided die is an icosahedron and rolls forever.
Under the microscope the virus is a clean icosahedron.