Present participle of pour; flowing or causing liquid to flow in a steady stream, or raining heavily.
From Middle English 'pouren,' of uncertain origin, possibly from Old French 'porer' meaning to sift or strain. The sense developed from the idea of liquid passing through something.
The phrase 'pouring over books' is often misspelled as 'pouring' instead of 'poring' - a confusion that creates the amusing mental image of literally dousing books with liquid while studying.
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