A theoretical or archaic term possibly referring to a type of mineral, stone, or material with helmet-like or cassida-like qualities.
From cassida (helmet) plus -ony (a suffix for stones or minerals, as in 'antimony'), though this word is extremely rare or possibly obsolete.
This word is so obscure that it might only exist in old mineral handbooks or alchemical texts—it's the kind of term that makes word historians excited because it reveals forgotten categorization systems!
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