A variant or archaic plural form of heptahedron, though non-standard in modern usage.
A historical or corrupted form mixing Greek 'hepta' + 'hedra' with redundant 'dra' ending. Appears in older texts but is considered incorrect in contemporary scientific nomenclature.
This word is a fascinating example of how scientific terminology evolves—early mathematicians sometimes created variant plurals before standardized conventions emerged, leaving these ghost words in old texts!
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