Either to fail to notice something or to ignore something intentionally; or to have a high view of something below.
From Middle English 'overloken,' 'over-' (above) plus 'look' (to see). The dual meanings both stem from the physical idea of looking down from a higher position.
Cognitive science calls the failure to notice things 'inattentional blindness'—like how you can overlook a typo in your own writing but a stranger spots it instantly because your brain expects it to say the right thing.
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