A hybrid or doubly-pluralized form combining Latin and English plural conventions, likely non-standard or obsolete.
This appears to be a double pluralization (effluvivia + -ums) or a hyper-correction in Early Modern English when speakers weren't sure which Latin rules to apply. Probably never widely established.
This word is a linguistic ghost—it probably existed in some scholar's writing but never caught on, showing how competing grammar rules can create odd hybrid words that die out because they're just too awkward.
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