The quality or state of being base; moral depravity, dishonor, or contemptible character.
From base (of low character) + -ness (Old English suffix forming abstract nouns). This nominalization has been used since Middle English to discuss shameful qualities.
Baseness is that special kind of badness that's not just a mistake or misfortune—it's choosing to act shamefully and dishonorably, which is why literature uses it to describe villains who know better but do wrong anyway.
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