The quality or state of having a blank or empty mind; absent-mindedness or lack of focus.
From blank-minded + -ness (noun suffix forming abstract qualities). The -ness suffix, from Old English, creates nouns from adjectives by indicating a state or quality.
The fact that we have a specific word for being blank-minded tells you something about human psychology—we're apparently absent-minded enough and frequently enough that we needed to name it, and medieval philosophers would have called it being 'unmindful of the present moment.'
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