icosahedron (English)
Where does "icosahedron" come from?
The English word 'icosahedron' derives directly from Ancient Greek 'eikosáedron'[1]. This compound brings together 'eíkosi', meaning 'twenty', with 'hédra', meaning 'face of a geometrical solid'[1]. Digging into their deeper origins, 'eíkosi' descends via Proto-Hellenic '*ewī́kəti' from the Proto-Indo-European numeral '*(h₁)wídḱm̥ti'[2], while 'hédra' traces back through Proto-Hellenic '*hédrā' to the Proto-Indo-European root '*sed-', meaning 'to sit'[3].
Open questions
- The initial laryngeal consonant in the reconstructed Proto-Indo-European form '*(h₁)wídḱm̥ti' remains uncertain. [2]
Full etymology tree
- icosahedron (English), 'A polyhedron with twenty faces.'
- borrowed εἰκοσάεδρον (eikosáedron) (Ancient Greek)
- compound εἴκοσι (eíkosi) (Ancient Greek), 'twenty'
- inherited *ewī́kəti (Proto-Hellenic)
- inherited *(h₁)wídḱm̥ti (Proto-Indo-European)
- inherited *ewī́kəti (Proto-Hellenic)
- compound ἕδρα (hédra) (Ancient Greek), 'seat, chair, stool, bench'
- inherited *hédrā (Proto-Hellenic)
- inherited *sedreh₂ (Proto-Indo-European)
- derived *sed- (Proto-Indo-European), 'to sit'
- inherited *sedreh₂ (Proto-Indo-European)
- inherited *hédrā (Proto-Hellenic)
- compound εἴκοσι (eíkosi) (Ancient Greek), 'twenty'
- borrowed εἰκοσάεδρον (eikosáedron) (Ancient Greek)
Descendants and derived words
- great icosahedron (English)
- hemi-icosahedron (English)
- icosahedronic (English)
- supericosahedron (English)
- truncated icosahedron (English)
Sources
- icosahedron (English) - Wiktionary
- εἴκοσι (eíkosi) (Ancient Greek) - Wiktionary
- ἕδρα (hédra) (Ancient Greek) - Wiktionary
Updated October 2026
Etymology data from Wiktionary, CC BY-SA 4.0 · About Miraris