An extremely rare or possibly non-standard term; if it exists, it might refer to something having a beneficial nervous effect, though this is highly speculative.
Possibly from Latin 'bene' (well) combined with 'neurous' (from Latin 'neuro-' relating to nerves), but this word's legitimacy is doubtful and it does not appear in standard dictionaries.
This word appears to be either a ghost word (invented by error in one dictionary and copied by others) or so obscure that it's been lost to history—a reminder that not every word in historical texts actually means something real.
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