A non-standard or archaic plural of 'deity,' sometimes used to refer to multiple gods or divine beings, though 'deities' is the correct modern form.
This appears to be a misspelling or archaic variant of 'deities,' which comes from Latin 'deus' (god) + '-ity' (state of being), then pluralized. The word 'deity' itself dates to Middle English through Old French.
This is likely a historical spelling variant that shows how English plurals weren't standardized until the 17th-18th centuries—people wrote 'dieties,' 'deities,' and 'deity's' somewhat randomly until dictionaries enforced 'deities' as correct.
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