The quality of being erroneous; the state of containing errors or being based on wrong assumptions.
From 'erroneous' plus the noun suffix '-ness'. 'Erroneous' comes from Latin 'erroneus', derived from 'errare' (to wander/err).
This is a formal word for being simply 'wrong'—using 'erroneousness' in an argument sounds much more academic than just saying 'that's incorrect!'
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