A plural or variant form, though this word is extremely rare or obscure in modern English and its precise meaning is unclear.
Possibly a plural form related to 'copia' (abundance) from Latin, or potentially a proper noun or specialized term, but the etymology is uncertain.
This appears to be an obscure or archaic word—it might exist in specialized dictionaries but has essentially disappeared from living English, representing the natural erosion that happens as languages evolve and discard words no longer needed.
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